262 



CAPE COD GEOLOGY 



by glacial and stream action during the Wisconsin stage. Most of the deposits 

 on it, however, are older than those of the Wisconsin stage. North of the clay 

 pounds at Highland Light the lower, oldest beds in that region can be traced 

 continuously northward into the bluffs of the lower plain — the Truro. The 

 Wellfleet plain appears to have been deeply dissected by westward flowing 

 streams before it was occupied by the Wisconsin ice. Some of the vales in this 

 plain headed in land that stood east of the present cliffs of the Cape, but 

 that is now washed away. The spaced erosion and the general parallelism of the 

 channels do not resemble the creases on the margins of the outwash plains 

 that were formed in front of the Wisconsin ice sheet on Nantucket and Marthas 

 Vineyard. At a place in the Eastham plain where Fresh Brook enters the salt 

 creek that occupies the greater part of a small valley there is a pamet 1 that is 

 unmodified by glacial action. 



Although it may be assumed that the stream erosion on the Wellfleet plain 

 was the work of water that flowed out of the ice sheet during its advance in 

 Wisconsin time, this assumption appears to be unwarranted, for the ice did 

 not entirely melt during the interval between the Nantucket and the Falmouth 

 substages, and the pamets were in existence when the ice sheets finally dis- 

 appeared. The bottoms of these channels, like those of the channels about 

 Chatham, lie below sea level and should be referred to the third stage of erosion 

 — that is, to the Vineyard interglacial stage. 



Great Hill, which stands northwest of Chatham village and rises to an 

 altitude of 132 feet, may be an outlier of the Wellfleet plain. Some of the areas 

 in the necks east of Orleans approach the 100-foot level and may be regarded 

 as tracts that were not worn down to the level of the Chatham plain. 



THE CHATHAM PLAIN 



Most of the eroded and thinly mantled surface of the Chatham plain stands 

 less than 80 feet above sea level. It lies within the Falmouth moraine, east of 

 Orleans. The surface about Chatham village declines to levels below 60 feet and 

 shows no trace of a break or cliff between a higher and a lower level. 



A large tract in which the topography is similar lies in Harwich, south of 

 Long Pond. Remnants of the Nantucket ice covered this tract so completely 



1 A pamet is a long depression in a thick deposit of stratified gravel and sand. In its course and slopes 

 it resembles a small valley formed by running water, but its sides and bottom have the forms of mounds 

 and hollows produced by irregularities in the deposition of glacial drift, either ice-laid or water-laid. Most 

 of these in Massachusetts occur in nearly parallel groups and occupy interlobate morainal tracts in the 

 Wisconsin drift. In the Plymouth woods such depressions merge into lines of inosculating kettle holes, 

 which are occupied by glacial lakelets, 



