314 



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Sketch of the Geology of 



still more remarkably broken and re-cemented by hem- 



Mas 



sachusetts ; which are described in my Report on the 

 Geology of that State. But I regard the subject as one 

 of the most obscure in geology. 



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It may not be amiss to notice here a remarkable rock, 

 which I recently met with in Rhode Island, on the west 



W 



I 



^'^ 



met with it only in large boulders; but have no doubt 

 that it occurs in the vicinity, in place ; since masses so 

 large could not have been removed many miles from their 

 native bed. At a little distance, this rock has precisely 

 the aspect of graywacke conglomerate. And indeed, it 

 is a conglomerate ; being filled with very distinct and 

 numerous rounded masses of that variety of (^uartz rock, 

 which takes a little mica into its composition, so as to 

 render It schistose. These masses have been as evidently 

 rounded by attrition as those in the most recent of the 



conglomerates ; or even 



as dikivial gravel. Yet the 



cement that holds the pebbles together is nothing more 



an 



crystalline aspect* And the rock is as firmly bound to- 



\ 



^ 



