--DISCLAIMER-- 
This report is preliminary and has not been reviewed for conformity with 
U.S. Geological Survey editorial standards or with the North American 
Stratigraphic Code. The use of trade, product, or industry names in this 
report is for descriptive or location purposes only and does not 
constitute endorsement of products by the U.S. Government. Opinions and 
conclusions expressed herein do not necessarily represent those of the 
USGS.



CONTENTS:

INTRODUCTION
GLACIAL CAPE COD
CAPE COD AND THE SEA
GEOLOGIC MAPPING
THE ULTIMATE CAPE COD
SELECTED READING



INTRODUCTION

Because of its exposed location, Cape Cod was visited by many early 
explorers. Although clear-cut evidence is lacking, the Vikings may have 
sighted this land about 1,000 years ago. It was visited by Samuel de 
Champlain in 1605, and his detailed descriptions and charts have helped 
present-day scientists to determine the rate of change of Nauset Beach 
Spit and Nauset marsh. Bartholomew Gosnold, a lesser known explorer, 
settle for a short time on the Elizabeth Islands to the southwest of Woods 
Hole and gave Cape Cod its name in 1602.

Figure 1 explanation: Index map of Cape Cod and the Islands, Massachusetts

The Pilgrims first landed in America on the tip of lower Cape Cod after 
they were turned back from their more southerly destination by shoals 
between Cape Cod and Nantucket Island. On Cape Cod, they found potable 
water and food and had their first fight with the natives. The Pilgrims, 
however, decided that this land was too sandy to support them, and they 
sailed across Cape Cod Bay to establish Plymouth. Today, the natural 
landscape of Cape Cod is little changed. Small villages are separated by 
large areas of forest, dune, beach, and marsh. This unspoiled natural 
beauty makes Cape Cod one of the most favored vacation areas for the 
people living in the thickly settled northeastern States.

The Great Ice Age (called the Pleistocene Epoch) began about one and a 
half million years ago. It is characterized by great ice sheets that 
advanced into the temperate regions of the Earth many times. These events 
are called glacial stages. Each glacial stage was accompanied by a 
worldwide lowering of sea level, because the glacial ice was made from 
water evaporated from the ocean basins. When these continental ice sheets 
melted away, during interglacial stages, the climate and sea level were 
probably much like they are today. In fact, many scientists believe that 
the Earth is presently in an interglacial stage and that ice sheets will 
once again advance into the temperate regions of the globe. If previous 
interglacial stages are used as an example, it suggests that the present 
interglacial is near its end and a new ice age is about to begin. However, 
man-induced global warming may alter this somewhat. 

As the last continental ice sheets melted away, the water returned to the 
ocean basins and sea level rose. Eventually, on Cape Cod, the rising sea 
began to drown the land left behind by the ice. Waves attacked the shore 
and eroded the glacial deposits. The sand was transported and redeposited 
by waves and currents to form bays protected from the open ocean by 
barrier spits and barrier islands. In the bays, marshes grew as the sea 
rose. The remaining glacial landforms and the landforms created by the 
rise in sea level make up today's landscape.


GLACIAL CAPE COD

The geologic history of Cape Cod mostly involves the advance and retreat 
of the last continental ice sheet (named the Laurentide after the 
Laurentian region of Canada where it first formed) and the rise in sea 
level that followed the retreat of the ice sheet. On Cape Cod, these 
events occurred within the last 25,000 years, and many can be dated by 
using radiocarbon techniques. 

Figure 2 explanation: shows the continental ice sheet advanced across Cape 
Cod to the islands about 23,000 years ago. Its maximum advance is marked 
today by gravel deposits on the continental shelf and by the outwash 
plains and moraines on the Islands. 

Figure 3 explanation: shows moraines and heads of outwash plains on 
Martha's Vineyard, Nantucket, and Cape Cod mark positions of the ice front 
during retreat. They also define lobes of the Laurentide ice sheet. The 
relationship between the deposits and lobes can be seen in this figure.

Figure 4 explanation: shows up ice aerial view of the Greenland icecap. 
This may have been the kind of view one would have seen flying over Cape 
Cod about 19,000 years ago . 

Sometime after 23,000 years ago, the glacier reached its maximum advance, 
a position marked approximately by the islands of Nantucket and Martha's 
Vineyard. The ice sheet was characterized by lobes that occupied large 
basins in the bedrock surface. These lobes were responsible for the 
location and overall shape of Cape Cod and the islands. Thus, the western 
side of Cape Cod was formed by the Buzzards Bay lobe, the middle part by 
the Cape Cod Bay lobe, and the lower or outer Cape by the South Channel 
lobe, which occupied a deep basin to the east of the Cape. During the 
maximum ice advance the landscape, where Cape Cod was soon to be, was 
glacial ice to the horizon 

Within a few thousand years or possibly less, the ice sheet started to 
retreat rapidly, and by 18,000 years ago, it had retreated away from Cape 
Cod and into the Gulf of Maine, which lies to the the east and to the 
north of the Cape. Thus the retreat of the ice from the islands to a 
position north of Cape Cod may have taken only a few thousand years. By 
roughly 15,000 years ago, the ice had retreated from the Gulf of Maine and 
all of southern New England. 

Figure 5 explanation: shows ice contact deposits of the Alaskan Malaspina 
Glacier. Till, boulders, and sand and gravel are underlain by the 
irregular surface of melting ice. Silt and clay are being deposited in 
ponds that occupy depressions in the ice surface .

The rock debris deposited by glaciers is called drift. It overlies bedrock 
that is similar to the hard rock that crops out throughout the rest of New 
England. On Cape Cod, the bedrock is buried by glacial deposits ranging 
from more than 200 to more than 600 feet thick. Drift consists of very 
fine to very coarse rock debris. If unstratified and unsorted, it is 
called glacial till. Till is deposited directly by ice and is unsorted 
because ice cannot separate rock fragments of different sizes. Thus, it is 
a mixture of all sizes of rock debris ranging from clay-sized particles to 
very large boulders. Stratified drift, on the other hand, is deposited by 
water which can separate the different sizes of rock fragments. The rock 
fragments are deposited in layers called strata. Gravel and sand are 
sorted and stratified by meltwater flowing in streams draining the 
glacier. The clay and silt-sized particles are carried by the meltwater 
streams into quiet water (glacial lakes or the sea) where they settle out 
according to the size of the particles; the coarsest, first, and the 
finest, last. 

Meltwater stream sediments that are laid down over and around glacial ice 
are called ice-contact deposits and generally consist of sand and gravel, 
but locally include silt and clay, till, and large to very large boulders. 

Figure 6: Geologic Map of Cape Cod Present Time: Marine, dune, and marsh 
deposits.

The distribution of the glacial deposits on Cape Cod is shown by the 
generalized geologic map. Most of the drift has been fashioned into either 
moraines or outwash plains. Both features mark positions of the ice front. 
Moraines are ridges of drift formed by moving ice. Most moraines are 
formed when the ice front remains more or less in the same place because 
advance of the glacier is balanced by melting along the ice front. 

When the debris falls free of the ice, it accumulates along the ice front 
much like material at the end of a conveyor belt. However, the Buzzards 
Bay and Sandwich moraines were formed in a different way. They were formed 
when an advancing ice front overrode sediments it had previously deposited 
or sediments that were older than the last glaciation. The advancing ice 
thrust sheets of drift upward and forward to form a large ridge beyond the 
ice front. Thus, the formation of the moraine more closely resembles the 
work of a bulldozer rather than a conveyor belt Figure 7 explanation: 
shows a model for the formation of the Buzzards Bay and Sandwich 
glaciotectonic end moraines by advancing ice. The thrust moraine is formed 
by adding thrust sheets at the base of the moraine. 

Figure 8 explanation: shows aerial view of the outwash plain in the 
Schuchert Valley, East Greenland. The outwash plain sediments are 
deposited beyond the ice front by streams of meltwater. The braided 
pattern is characteristic of meltwater streams because sediment loads are 
high and water the volume varies with the amount of melting. 

Outwash plains make up most of the Cape Cod landscape. They are made up of 
sand and gravel deposited by meltwater streams that flowed across the 
plain in a braided pattern This resulted in a broad flat depositional 
surface that sloped gently away from the ice front. The deposits in the 
ice proximal part of the outwash plain were deposited atop the glacial 
terminus, and when the ice melted away, these deposits collapsed to form 
an irregular surface that sloped steeply in an up-ice direction. This 
slope is called an ice-contact head of outwash. 

Outwash deposits also form a highly irregular and unorganized morphology 
called kame and kettle terrain. A kame is a knoll or hill composed of 
outwash deposits, which originally filled a hole in the ice.When the ice 
melted away, the deposits collapsed to form a hill. A kettle is just the 
opposite of a kame. The outwash was deposited around and over an ice 
block. When the ice block melted away, the outwash collapsed to form a 
hole. 

Figure 9 explanation: shows cross sections showing the relationship of a 
buried glacier ice front and buried ice blocks and the collapsed head of 
outwash and kettles. 

Only the outwash plain that forms eastern half of the upper Cape Cod still 
has an ice-contact head. Ice-contact heads of outwash plains on western 
half of upper Cape have been incorporated into the Sandwich moraine; those 
of outwash plains on lower Cape have been destroyed by wave erosion. 

Figure 10 explanation: shows Cape Cod Canal located in the drainage way of 
Glacial Lake Cape Cod. The water draining the lake downcut through the 
Sandwich moraine and flowed down the Buzzards Bay valley.. 

Most, if not all, of the outwash plains were formed as deltas in glacial 
lakes. The outwash plains on the upper Cape were formed in glacial lakes 
that occupied Nantucket Sound and Vineyard Sound, and those on the lower 
Cape were formed in a lake that occupied Cape Cod Bay. This is the best 
known of all the glacial lakes because outwash deltas graded to the lake 
occur all around Cape Cod Bay from Duxbury to Truro. Thus, the lake was 
given the name Glacial Lake Cape Cod. The earliest levels of the lake 
ranged between roughly 80 and 50 feet above present sea level, and during 
these lake stages, the lake drained across the Sandwich moraine and into 
the lowland that was to become Buzzards Bay. As the Cape Cod Bay lobe 
retreated northward, lower outlets were occupied and eventually the lake 
drained completely. The initial outlet across the Sandwich moraine was 
continuously lowered by erosion as the water escaped, and when the outlet 
was eroded to an elevation of about 30 feet, the outlet was abandoned. 
This low divide across the Sandwich moraine made it the obvious location 
for a canal connecting Cape Cod Bay and Buzzards Bay, a conclusion reached 
by both Miles Standish and George Washington. However, the first canal was 
not completed until 1914, and the improved canal (built and operated by 
the U.S. Army Corps of Engineers) was completed in 1940. 

Figure 11 explanation: shows Doane Rock located just off Nauset Road, 
Eastham is the largest glacial boulder on Cape Cod. Pits dug at the base 
showed as much rock below the surface as above. A boulder this large could 
only be deposited directly from glacial ice. 

Many other features on Cape Cod owe their existence, at least in part, to 
glaciation. The most common feature may be the large to very large 
boulders scattered about the glacial surface, usually in the moraines or 
ice contact terraine. These glacial boulders are too large to have been 
carried by running water and thus must have been deposited directly by the 
ice. Doane Rock in Eastham is the largest glacial boulder known on Cape 
Cod, and pits dug at the base showed as much rock below the surface as 
above. 

Figure 12 explanation: shows Ashumet Valley in Falmouth is typical of 
valleys cut into outwash plains by spring sapping. The lower reaches have 
been drowned by sea-level rise and upper reaches are commonly the sites of 
cranberry bogs.

Perhaps the most intriguing features related to glaciation are the valleys 
eroded in the outwash plains. The valleys are relict because most do not 
contain rivers or streams. They are dry, except where their lower reaches 
have been drowned by the rise in sea level. The origin of these valleys is 
complex. They most likely were formed by a process called spring sapping. 
This occurs when the water issuing from a spring carries away loose sand 
and gravel and causes the spring to migrate headward carving a long 
straight valley. In the case of the outwash plain valleys on Cape Cod, 
some special conditions were required. Presently, there are few springs on 
Cape Cod, because in almost all places the outwash deposits are very 
permeable and the upper part of the outwash plain deposits is dry. In 
order for the spring sapping to have occurred, a higher than present water 
table is required. This could be accomplished by glacial lakes with 
altitudes well above present sea level being dammed by the outwash plains. 
The best example would be Glacial Lake Cape Cod that was dammed by the 
outwash plains and the Sandwich moraine on upper Cape Cod. The high lake 
levels would cause a rise in the water table that, in turn, would cause 
springs to form on the outwash plains. There is evidence for a glacial 
lake to the east of the lower Cape outwash plains in the form of the silt 
and clay beds exposed in the cliff below Highland Light in Truro. Nothing 
more is known of this lake, but it may have provided a higher than present 
water table to allow spring sapping to form the valleys in the lower cape 
outwash plains. 

Figure 13 explanation: shows how Pamet River Valley in Truro is cut into 
the Wellfleet outwash plain and completely crosses lower Cape from Cape 
Cod Bay to the Atlantic and is thought to have formed when a headward 
eroding spring sapping valley intersected the glacial lake to east of 
lower Cape Cod and caused the lake to drain catastrophically. 

The Pamet Valley in Truro is wider and deeper than all other valleys on 
Cape Cod. The original floor of the valley, made up of glacial outwash, is 
well below sea level and overlain by mostly salt marsh deposits. The Pamet 
Valley may have started out like all other spring sapping valleys, 
however, the extreme width and depth of the valley requires further 
explanation. It is likely, that headward erosion by spring sapping cut 
completely across the Wellfleet outwash plain, reaching the outwash dam 
holding in a glacial lake to the east of the lower Cape. The breach caused 
the lake to drain catastrophically. This great flood carried away vast 
amounts of outwash to widened and deepened the original spring sapping 
valley.

Figure 14 explanation:. shows Great Pond in Wellfleet. This kettle pond 
marks the site of a large ice block left behind by the retreating South 
Channel lobe. The original kettle hole was far from round, but wave 
erosion and deposition along the shore have trimmed off headlands and 
closed off embayments in the shoreline much as they do along the ocean 
shore. 

Depressions in the outwash plain are called kettle holes. They mark the 
site of ice blocks that were left behind by the retreating glacier and 
buried by the outwash deposits. The buried ice was well insulated from the 
warmer post-glacial temperatures and may have persisted for several 
thousand years Kettle holes that are deep enough to expose the water table 
contain ponds or lakes. Similar to the ocean shore, waves have eroded 
sections along the shore to form cliffs and the eroded sand and gravel 
have been carried along the shore and deposited across reentrents in the 
shoreline. These low ridges composed of beach sand are called baymouth 
bars. In many kettle ponds, these processes have smoothed the shoreline so 
that the ponds are almost circular. 

Basal organic sediments in kettle ponds have been carbon dated. The oldest 
ages are on the order of 12 thousand years. These early dates appear to 
occur in kettles that are underlain by fine sediments, which prevented or 
impeded the percolation of rain and snow melt. Other kettle pond basal 
sediments are much younger and appear to indicate the time when the rising 
water table, caused by the rising sea level, first intersected the floor 
of the kettle hole.

Figure 15 explanation: shows Aerial photo of the embayed coastline from 
Nauset to Chatham. The drowned lows were formed when buried ice of sublobe 
of South Channel lobe melted out. Headland erosion to north of Nauset and 
longshore transport have formed the barriers and closed off the 
embayments. 

The indented coastline from Eastham southward to Chatham also owes its 
existence to the Laurentide ice sheet. Most likely, it represents the last 
remnant of an irregular coastline made up of headlands and embayments that 
marked the eastern limit of the glacial Cape. It also represents a western 
expansion of the South Channel lobe in the form of a sublobe, which at its 
largest size, occupied the site of the Eastham outwash plain as well as 
limiting the eastern extent of the Harwich outwash plain and the 
distribution of the Nauset Heights deposits. 

Figure 16 explanation: shows wind-polished stone or ventifact. These 
fluted, faceted, and pitted stones were shaped by wind driven sand, silt, 
and clay particles as they sat on the outwash plain surface. Later they 
were worked upward into the eolian layer by frost action. The unusual 
shape of some ventifacts cause them to be mistaken for Indian artifacts by 
laymen. 

At the end of glaciation and before the landscape was well covered with 
vegetation, winds blowing across the barren glacial deposits, including 
material from the exposed bottoms of drained glacial lakes, picked up 
sand, silt, and clay and deposited this material as a thin almost 
continuous blanket on the drift surface. Stones lying on the drift surface 
were cut, faceted, and polished by sand blasting. These stones, called 
ventifacts, have been moved into the windblown layer by frost action. They 
are distinctively shaped and some have been mistaken for tools of Indian 
origin.

The windblown material and the upper part of the underlying drift make up 
the parent material for Cape Cod soils. These soils are called podzols and 
are typical of young soils developed on a sandy parent material in a 
temperate climate under forest cover. A podzol is characterized by a soil 
profile that consists of an upper dark organic zone and a bone-white zone 
that together make up the "A" horizon and a reddish orange zone that makes 
up the "B" horizon. Beneath the "B" horizon is the parent material of the 
soil, either drift or the windblown layer or both. 

Figure 17 explanation: shows a Cape Cod podzol soil. From top to bottom 
the soil consists of an "A" horizon made up of the organic litter zone and 
the leached zone (light colored zone), and the dark colored reddish orange 
"B" horizon. The "B" horizon is underlain by the parent material. 


CAPE COD AND THE SEA 

During the Laurentide glaciation and for some time after the retreat of 
the ice away from Cape Cod, worldwide sea level was about 400 feet below 
its present level. Much of the continental shelf to the south of Cape Cod 
was dry land, as was Georges Bank to the east and Stellwagen Bank to the 
north. However, the sea was never far away from the lower Cape following 
the retreat of the ice, because, as the ice retreated away from Cape Cod 
and into the Gulf of Maine, it was immediately replaced by sea water. 

Figure 18 explanation: For some time after the retreat of the ice the sea 
remained several hundreds of feet below its present level. The land shown 
in brown was exposed by the lowered sea level shortly after the retreat of 
the ice from southeastern Massachusetts. As the ice melted, the sea rose 
gradually. Only the area shown in yellow is above sea level today. 

This occurred because of deep basins in the Gulf of Maine, which are close 
to the lower Cape and because the weight of the glacial ice had depressed 
the crust in the Gulf of Maine to below the world wide low sea level. 
Thus, the lower Cape Cod has had a maritime environment since about 19,000 
years ago. 

Figure 19 explanation: shows a Mastodon and calf. Many of the plants and 
animals that live on Cape Cod today as well as extinct animals such as 
mastodon and mammoth survived the ice ages by occupying the emerged 
Continental Shelf south of the ice front as well as ice free regions 
throughout North America south of the glacial limit. This mastodon and 
calf are part of a life-size diorama at the New York State Museum in 
Albany. 

Mastodon, mammoth, and other extinct animals of the Pleistocene Epoch, and 
most, if not all, of the animals and plants that now live in northeastern 
North America, survived the Laurentide glaciation on the exposed 
continental shelf. Evidence for the presence of mastodon and mammoth is 
provided by the numerous teeth dredged from the sea floor of the 
continental shelf and the Gulf of Maine. 

Figure 20 explanation: shows Mastodon and mammoth teeth dredged from 
submerged continental shelf provide evidence that these animals lived 
south of Laurentide ice sheet. These teeth came from Gulf of Maine north 
of Cape Cod indicating that these and other animals migrated northward as 
the ice sheet retreated.

Early people called Paleoindians may have lived on the exposed shelf about 
11,000 years ago. Both plants and animals migrated northward as the ice 
retreated and as the rising sea level inundated the continental shelf. 

As the continental ice sheets melted around the globe and the water 
returned to the ocean basins, sea level rose. At first the sea rose 
quickly, about 50 feet in 1,000 years. As glacial ice volumes became 
reduced, the rise in sea level gradually slowed. On Cape Cod, the rate of 
sea-level rise between 6,000 years ago and 2,000 years ago was about 11 
feet per 1,000 years. From 2,000 years ago, the rate of sea-level rise was 
about three feet per 1,000 year. Rates of worldwide sea-level rise were 
determined using radiometric ages of submerged shoreline features. Local 
rates of sea-level rise have been determined by radiocarbon dating of salt-
marsh peats that are an accurate indicator of sea level.

By about 6,000 years ago, the rising sea reached the cape and wave erosion 
of the glacial deposits began. At first, headlands composed of glacial 
drift, east of the present eastern shore of the Cape, began to erode as 
waves attacked the fragile land to form marine scarps or sea cliffs. The 
sea, however, does not simply destroy the land 

Figure 21 explanation: Map A shows the glacial Cape about 6,000 years ago, 
before extensive wave erosion of the glacial deposits had occurred, and 
Map B shows the present pattern of erosion is shown with shoreline 
undergoing wave erosion and shoreline undergoing deposition. However, in 
many places, the shoreline of the depositional features is migrating 
landward. 

Much of the eroded material is reworked and transported along the shore by 
longshore drift and longshore currents generated by the oblique approach 
of the waves. This transported material is redeposited along the shore to 
form new land. The sand is transported and redeposited to form bay mouth 
bars, spits, and barrier islands across embayments in the coastline. 

Figure 22 explanation: shows an aerial view photo of Wellfleet Harbor and 
a diagram. Wellfleet Harbor which occupies a depression that was formed 
when ice, possibly a sublobe of the South Channel lobe, prevented outwash 
deposition. The diagram shows areas of the following: 1) the islands which 
are composed of Wellfleet outwash plain deposits that filled holes or 
depressions in the ice. The islands are tied together and to the mainland 
by spits called 2) tombolos which are composed of sand eroded from the 
cliffed Cape Cod Bay shore to the north of the harbor. Once the tombolos 
were in place, they provided protection from waves and 3) marsh deposits 
formed in the sheltered water . 

At this time, the coastline may have resembled the present coastline from 
Eastham southward.

Figure 15 explanation: shows Aerial photograph of the embayed coastline 
from Nauset to Chatham. The drowned lows were formed when buried ice of a 
sublobe of the South Channel lobe melted out. Headland erosion to the 
north of Nauset and longshore transport have formed the barriers and 
closed off the embayments. 

These features were the forerunners of the present Provincetown spit and 
the barrier islands of Eastham, Orleans, and Chatham. In Cape Cod Bay, 
wave erosion of headlands and formation of the spits, including the spits 
called tombolos that connect the Wellfleet Harbor Islands and protect the 
harbor from the open ocean, probably started somewhat later. 

Figure 24 explanation: shows an air photo of parabolic (U-shaped) dunes on 
Provincetown Spit. The view is from west to east. Prevailing westerly 
winds have blown out the centers of the dunes so that they open to the 
west. 

Figure 23 explanation: shows an aerial view of Sandy Neck barrier beach 
and the Great Marshes at Barnstable. The barrier was built by wave-
generated longshore drift, longshore currents carrying sand derived from 
the cliffed glacial deposits to the west, and onshore winds carrying sand 
inland to form the sand dunes about 4,000 years ago as the rising sea 
drowned the glacial cape. 

Sandy Neck is thought to have formed around 4,000 years ago when relative 
sea level stood a little more than twenty feet below present. Many spits 
shelter a quiet body of water called a lagoon. Associated with the lagoon 
are salt marshes and sand or mud flats. The spits also form the foundation 
for coastal sand dunes, the best examples of which occur in the 
Provincetown and Truro area and on Sandy Neck. 

The combination of spit, lagoon, salt marsh, and sand dune make up what is 
called a barrier island. "Barrier Island" is a generic term that also 
includes barriers tied to headlands. The growth and development of these 
features as well as the lagoon are closely related to the growth of the 
protecting spit. For example, Sandy Neck in Barnstable has grown during 
the past 3,000 years from a spit a little over 1 mile long protecting a 
small lagoon and a few patches of marsh to a barrier island 6 miles long 
protecting a large lagoon and a marsh of several square miles. 

Figure 25 explanation: shows stages in the development of Sandy Neck spit 
and the Great Marshes west of Barnstable from 3,000 years ago to present 
time. The marsh grew upward in response to the rising sea and laterally in 
response to the growth of the spit. The maps, ages, and relative sea level.

Once formed, spits and barrier islands do not remain unchanged for long. 
The forces of waves and wind continue to transport and redeposit the beach 
and dune deposits. The eroded material carried by the waves and currents 
is washed into the lagoon during northeast storms and hurricanes to form a 
new foundation for the dunes. In this manner, the barrier islands migrate 
landward. Without this landward migration, in response to the rising sea 
level, the spits and barrier islands would drown. Strong onshore winds 
also transport sand inland where it is deposited to form dunes. On young 
spits, the dunes are usually small, but on mature barrier islands, such as 
Sandy Neck, Monomoy Island, and Provincetown, the dunes reach heights of 
40 to 100 feet. The dunes themselves are attacked by the wind and, where 
unprotected by vegetation, continuously change shape. For example, the 
parabolic dunes in Provincetown and Truro are formed when the prevailing 
west wind blows out the middle of an existing dune. In the past, the dunes 
were covered by mature forest and were stable. A remnant of this cover, 
the beech forest, can be seen in Provincetown. Unfortunately, sand 
transported from adjacent unstable dune areas is slowly burying the 
forest. Elsewhere, evidence of past forest cover is the forest floor 
layers exposed by the wind in the unstable dunes. On sandy Neck, flint 
chips, charcoal, and hearth stones from Indian encampments are associated 
with some of the exposed forest floor layers. 


GEOLOGIC MAPPING ON CAPE COD

Our understanding of the geology and geologic history of Cape Cod is 
largely based on field studies done to produce U.S. Geologic Survey 7 1/2-
minute geologic quadrangle maps. Initial mapping was done in the late 
1930`s and took place in western Cape Cod. Geologic quadrangle mapping was 
resumed from 1964 to 1967 in response to the establishment of the Cape Cod 
National Seashore and the final quadrangle maps were completed between 
1969 and 1972. The geologic quadrangle maps of Cape Cod and geologic maps 
of Martha`s Vineyard and Nantucket were used to compile a 1/100,000 scale 
geologic map of the Cape and Islands (Map I-1763) published by the U.S. 
Geological Survey in 1986 and reprinted in 1995. Geophysical and water 
resource surveys, in addition to the geologic mapping, have allowed the 
identification and location of the natural resources of Cape Cod and how 
best to use them. Today, the most valuable natural resources of the Cape 
are related to tourism and recreation. These include beaches along the 
seashore and lakes and ponds and harbors for recreational boating. Cape 
Cod has abundant fresh water, but it is increasingly threatened by 
pollution, especially in western Cape Cod. Other threats to the natural 
environment include attempts to control shoreline erosion and retreat, the 
increasing population, and all the development needed to support the 
increase. Careful planning will be needed to preserve what is good about 
Cape Cod and insure that future generations will have access to the 
beaches, harbors, wetlands, lakes and ponds, forests and open space.


THE ULTIMATE CAPE COD

The forces of marine erosion will continue to attack Cape Cod and the land 
will eventually be worn away. New lands built by waves, currents, and 
winds will not balance the loss of land to the sea. We can guess the rate 
of loss based on a few things we know. For example, we know that the 
cliffed ocean side of lower Cape Cod loses about 5 acres a year to marine 
erosion. New land constructed from this eroded material averages about 1 
acre a year. Thus for each acre lost, less than half an acre is gained. 
Estimates for other parts of the Cape may very greatly from this figure. 

Figure 26 explanation: Billingsgate Island before the entire island was 
eroded away. It is clear that shore erosion is threatening the lighthouse 
as the sea wall of boulders was built in a futile effort to protect the 
lighthouse from wave attack. Unfortunately, the sea wall was poorly placed 
and actually increased the rate of erosion. Photograph provided by the 
Cape Cod National Seashore.

But, at some distant time--not for many generations, however--Cape Cod may 
be nothing more than a few low sandy islands surrounded by shoals. It 
might be like Billingsgate Island that, in the middle 1800's, was about a 
mile long and about a half a mile wide and included about 30 homes, a 
school house, and a lighthouse. 

Today, Billingsgate island is a shoal that is exposed above sea level only 
during the lowest tides. 

Figure 27 explanation: The remains of Billingsgate Island of Wellfleet. 
Photographed at about low tide in 1991. Today all that remains of the 
island is a shoal exposed during very low tides. Blocks of stone behind 
the boulders of the original riprap sea wall are all that remain of 
Billingsgate lighthouse. The fate of Billingsgate Island may be a 
precursor for Cape Cod as the sea continues to erode the fragile land. 

The future Cape Cod could also be like Stellwagen Bank just to the north 
of Provincetown and be completely submerged. Nothing may be left to supply 
a group of hungry tourists with drink, food, or even an opportunity to 
fight with the "natives." 


SOME BOOKS AND MAPS ON THE GEOLOGY AND NATURAL HISTORY OF CAPE COD

Chamberlain, B. B., 1964, These fragile outposts: Doubleday. Reprinted, 
Parnassus Imprints (1981), Yarmouth Port, Massachusetts, 327 p. 

Finch, Robert, undated, Cape Cod , its natural and cultural history: U.S. 
National Park Service Handbook 148, 111 p.

O'Brien, Greg, ed., 1990, A guide to nature on Cape Cod and the Islands: 
Viking Penquin, New York, 240 p. 

Oldale, R. N., 1981, Geologic history of Cape Cod, Massachusetts: U.S. 
Geological Survey Popular Publication, 23 p.

Oldale, R. N., 1992, Cape Cod and the Islands, the geologic story: 
Parnassus Imprints, East Orleans, Massachusetts, 208 p.

Oldale, R. N., and Barlow, R. A., 1986, reprinted 1995, Geologic map of 
Cape Cod and the Islands, Massachusetts: U.S. Geological Survey 
Miscellaneous Investigation Map I-763, scale 1/100,000.

Strahler, A. N., 1966, A geologist's view of Cape Cod: Doubleday. 
Reprinted Parnassus Imprints (1988), Orleans, Massachusetts, 115 p.