CAPE COD GEOLOGY 



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divided into three smaller ones and drift filled the channels between them. 

 On the southeast side of the southern pond an ice-contact terrace and outwash 

 plain shows that a sand plain was formed in a space left by the melting of the ice. 



Another group of ice-block holes in the town of Sandwich, near Farmers- 

 ville, including Spectacle, Triangle, Lawrence, and Hog ponds, further illustrates 

 the mode by which the remnants of the Nantucket ice sheet were broken up by 

 the opening of channels that were filled with gravel and sand, here perhaps 

 largely by outwash from the Falmouth ice front, for the frontal plain of that 

 substage encloses these holes. 



A lakelet in the bottom of one of these depressions may occupy a lower story, 

 so to speak, in a group of depressions. On one or more sides of such a lakelet 



OUTWASH PLAIN 



Fig. 21. — Section of Falmouth moraine and outwash plain, showing old ice blocks in sites of glacial lakelets. 



there is a terrace whose surface lies at the foot of a higher bank, or ice- contact 

 slope, showing that the space around a large mass that had melted had been 

 filled by gravel and sand to a certain height before the ice block disappeared. 

 Such a terraced kettle or ice-block hole may be seen in Wakeby Pond, in 

 Sandwich. 



The close alignment of the ice blocks and their somewhat regular spacing 

 suggests that broad waterways existed between remnants of the ice sheet in 

 the first clearly defined stage of its final disappearance and that cross channels 

 were afterward formed by melting, so that the long ridges were broken up into 

 huge blocks, roughly half a mile to a mile and a half across. The long axes of the 

 holes, as shown by the shapes of the lakelets, trend southward through Falmouth, 

 Sandwich, and Barnstable, though departures from this general trend are shown 

 by ponds that extend south westward. Farther east, in Yarmouth and Harwich, 

 the southwestern orientation of the long axes becomes a pronounced feature, 

 not only in individual ponds but in groups of ponds. In its northern half Bass 

 river, a connected series of ice-block holes and channels, trends southeastward, 

 but it turns abruptly at South Dennis. This orientation of topographic features 

 was due to the structural control resident in the moving glacier or in the ground 

 on which it lay. Along the lobes of many existing glaciers there are crevasses 



