The Geology of H Ingham. 



49 



striae, though probably exposed there to the elements for centu- 

 ries. These lines are northwest and southeast, and south 30° 

 east. Other lines on a neighboring rock are northwest by west 

 and southeast by east. On the westerly side of the bay granite 

 appears in a high cliff towards and extending into the water. 



By ascending this cliff, passing over it to its western declivity 

 and descending to the narrow beach at its base, which should be 

 done at low tide, a dike exposure may be seen of much interest. 

 It is what is called a double dike, the molten material having 

 made its way to the surface within two contiguous joints in the 

 granite. The larger portion has a width of about eight feet, the 



Figure No 3. 



smaller one about one foot, and they are separated by about one foot 

 of the invaded rock. See Figure No. 3. This double dike slopes 

 to the south from the vertical at an angle of 45°. This is the 

 extreme western end, on Rocky Neck, of the dike first mentioned 

 as appearing on the eastern shore. It does not present there 



VOL. I. 



