172 SIDNEY POWERS 



Firth of Forth, Scotland, quartz diabases owe their free siHca to 

 solution of acid country rocks in normal diabase and contain cor- 

 roded quartzose inclusions.^ 



Ogunquit, Maine: About 2 miles south of Ogunquit, Maine, 

 several inclusion-bearing sills are exposed on the seashore halfway 

 between Perkins Cove and Bald Head. The rocks of the region 

 consist of thick-bedded slates, tilted into a vertical position with 

 a uniform northeast strike, cut several miles inland by .biotite 

 granite. The slate is intruded by vertical trap sills of two or three 

 generations, the older ones being porphyritic. The sills are mostly 

 5 feet or less in width, but one is over 50 feet wide. Most of the 

 inclusion-bearing sills are of this older porphyritic type, which is 

 seen under the microscope to be an augite-biotite kersantite. The 

 sills occasionally cut across the bedding of the slates. They are 

 younger than the frequent quartz veins which cut the slate. 



In many of the sills in the vicinity there are a few inclusions. 

 The latter are often 6 to 8 inches in length, with their longer axes 

 parallel to the sides of the sill. In one sill, 2 feet, 10 inches wide, 

 are two rounded inclusions of coarse graphic granite about 16 and 

 12 inches in diameter respectively, an angular block of granite 16 

 inches long and about 3 inches wide, with smaller subangular frag- 

 ments of quartz and granite. There is a fused contact around all 

 these inclusions. A 7 -foot sill contains in one place many small 

 subangular and rounded fragments of quartz, granite, syenite, and 

 slate. 



The principal inclusion-bearing sill is exposed for about 400 

 feet, showing a variation in width from 3 to 5 feet. It runs parallel 

 to the stratification and has resisted erosion by the sea, while the 

 slates on one side have been eroded away. The sill is cut by two 

 younger dikes. 



The character of the inclusions varies greatly. They are com- 

 posed, in order of relative abundance, of a moderately coarse- 

 grained light-colored syenite with green hornblende as the dark 

 constituent; a coarse-grained granite resembling the syenite but 

 containing free quartz; fine-grained pink and white apHtic granites 

 which are probably biotite granites; fine-grained syenite seen in 



' E. Stecher, Tschermak's Mitt., IX (1888), 193. 



