CAPE COD GEOLOGY 



3. Sculpturing of the surface during times when it was exposed to stream 

 erosion. 



4. Slight erosion and mantling by thin sheets of drift of the last glacial 

 incursion. 



The nearly flat outwash plains that border the moraines rise from near sea 

 level to an altitude of about 100 feet on Marthas Vineyard and about 60 feet 

 on Nantucket. Their gentle southward slopes bear well-defined creases, which 

 become deeper and wider southward, suggesting channels that were once occu- 

 pied by running streams. 



The relief of Cape Cod is due in part to action similar to that shown on 

 Nantucket and Marthas Vineyard, and the beds that stand above sea level have 

 been exposed to the action of the same agents of deposition and erosion that were 

 in operation on these islands. A belt of morainal topography of the knob and 

 basin type, without bordering outwash plains, is seen in the Elizabeth Islands. 

 This morainal belt is traceable on the mainland from the southwestern heel of 

 Cape Cod, at Wood's Hole, north-northeastward to the Cape Cod Canal, from 

 which it extends eastward in the form of a rounded, hilly ridge along the south 

 shore of Cape Cod Bay, gradually declining in elevation until, near the east 

 coast, its features merge into those of glacial plains. South of this morainal belt 

 a glacial outwash plain forms most of the surface, the striking features of which 

 are numerous pits and glacial lakes. This outwash plain rises toward the north- 

 west in an interlobate angle between the morainal belts in the form of a large 

 outwash fan, which reaches an altitude of 220 feet above the sea at its junction 

 with the line of glacial deposits that were laid down directly at the front of the 

 ice sheet. 



The surface of Cape Cod from the vicinity of Orleans northward may be 

 divided into three tracts, which include glacial plains, though in the middle tract 

 deep kettles and the glacial channels known as "hollows" mask the features of 

 the plain. The northern and the southern tracts stand 60 to 70 feet above sea 

 level and decline gently westward, toward Cape Cod Bay. The middle tract, 

 which rises toward the outer coast, exceeds 100 feet in altitude in much of its 

 area, reaching at some places an altitude of 140 feet. It forms the wildest and 

 most picturesque part of the outer shore of the Cape, which presents to the storms 

 of the Atlantic high bluffs of yellowish gravel and sand. 



The outstanding projections in the surface of the Cape and of the islands 

 south of it mark the sites of great terminal moraines^ which are traceable west- 

 ward to New York City and eastward to the coast of New England. Nantucket 



