24 



HISTORY OF COH ASSET. 



An impressive example of these two distinct series of 

 east-west dikes is to be seen exposed on the easterly end 

 of Beach Island, near the outlet of Little Harbor on the 

 sea side of the island. One dike about three feet thick 

 has been cracked lengthwise irregularly, and another dike 

 about one foot wide has crowded its way up through the 

 first ; so that although they are both diabase and both 

 running in the same general direction, the smaller is 

 plainly a later eruption than the other. 



There was still a third and later eruption of lava through 



The Dike at White Head. 



our Cohasset rocks. Whether it came as long after the 

 others as hundreds or even thousands of years there is no 

 way of knowing. 



The direction of these last is about north and south, and 

 Professor Crosby has counted ten of them between the 

 Black Rock House and White Head. 



The most notable of all these is the familiar one on Lit. 

 tie White Head. Sailboats going into the harbor are in 

 easy sight of it. The countless picnics of our summer 



