SOME INSTANCES OF MODERATE GLACIAL EROSION 167 



along both the vertical and horizontal joint planes, has produced a 

 gravel of disintegration to a depth of five feet and with a width, in 

 one or two places, of eighteen inches. By it the granite has been 

 separated into rounded, bowlder-like blocks incased in disintegrated 

 granite gravel exactly like those revealed in quarries in Maryland 

 where the granite is covered by a residual soil. 



Fig. 4. — Disintegration of granite along joint planes at Lanesville, Cape Ann, 

 Mass. Gravel underlies these bowlders, which are in place. 



Nowhere on the Cape is so good an instance of decay found as 

 this; but in dozens of places decayed gravel occurs along the joint 

 planes, in one or two instances to a depth of five feet. These localities 

 are found in all parts of the Cape, and on both stoss and lee slopes. 

 In a number of places granite masses that are thus partly incased 

 in gravel are scratched and polished on the surface, showing how 

 slight has been postglacial decay, and proving that the disintegration 

 farther down cannot be postglacial. 



