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Portland and its Vicinity. 315 



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gether as the most solid varieties of mica slate. In fact, 

 it is a mica slate conglomerate. In my Report on the 

 Geology of Massachusetts, I have described a la 

 posite of a rock, differing from this only in the substitu- 

 tion of talc for mica, occurring on the eastern side of 

 Narraganset Bay, near Newport, and on the eastern 

 border of the graywacke formation. This mica slate 

 condomerate occurs alon<r the western border of the same 



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formation, where it adjoins quartz rock, mica slate, and 

 gneiss. Do not such rocks as these conglomerates and 

 the quartzose breccias that have been noticed, lend a 

 strong confirmation to the theory, which supposes the 

 primary stratified rocks to be only metamorphic second- 

 ary ones ? Between these mica and talcose slate con- 

 glomerates, and genuine classical graywaCike, I found, in 

 Rhode Island, almost every variety of gradation. 



Limestone^ 



As we go over the arm of the sea that separates Port- 

 land from Cape EHzabeth, not far from the southeastern 

 extremity of the bridge, we meet with an imperfect sort 

 of limestone ; or, it is limestone with a large mixture of 

 the talcose and mica slates that have been described. Its 

 color is blue, and it is traversed by veins of white calca- 

 reous spar ; and sometimes we meet whh thin layers of 

 milky quartz. It bears a strong resemblance to some of 

 the limestone that is brought from Thomastown in Maine, 

 and which is used as marble. And if slabs of sufficient 

 size can be obtained, I do not see why It will not form a 

 handsome variegated marble. At present, it is laid bare 

 only in two or three places along the shore ; and not im- 

 probably, it may be found more free from fissures, and less 



