LOCATION' AND TOPOGRAPHY 439 



of postglacial development. The Blackstone River flows through granite 

 and hard quartzite, but the course of this river was determined in pre- 

 glacial times by the strike of the bedding and of the schistosity of the 

 rocks. Both the bedding and schistosity in this locality trend in a north- 

 west-southeast direction. 



The effect of Pleistocene glaciation has been to modify the topography, 

 scouring off the hills and filling the valleys. Prof. N, S. Shaler esti- 

 mated that at least 200 feet of cumberlandite had been removed from the 

 top of Iron Mine Hill by the various glacial advances. He traced the 

 boulder train from this hill for 60 miles.® 



In the region west of the Blackstone Eiver and in the district north of 

 Grants Mills the bedrock is quite effectually concealed under glacial de- 

 posits consisting largely of stratified gravels ; also the Carboniferous sedi- 

 ments are covered with glacial material, making it impossible to trace 

 out the boundary of the Bellingham series. 



Postglacial erosion has removed less than an inch from the softer rocks 

 of the region and weathering has in general penetrated the granites for a 

 distance of only a few inches. Glacial striae have in general been removed 

 from the rocks. In the pre-Cambrian conglomerates the glacially pol- 

 ished hard pebbles stand out in relief from the softer matrix. 



Summary Table of Rock Formatioi^s 



Followmg IS a concise summary of the formations in the area under 

 consideration : 



Sedimentary rocks. 

 Pre-Cambrian. 



Cumberland quartzite, Including interbedded schist. 

 Asliton schist, including ehlorite-epidote schist, hornblende schist, 

 blue quartz schist, and interbedded Smithfield limestone. 

 Lower Cambrian. 



Limestone fossiliferous boulders, red and light yellow shale, and some 

 fragment of quartzite. 

 Pennsylvanian. 



'Narragansett series. 



Wamsutta red beds, including conglomerates, shales, and sand- 

 stones of red color. 

 Pawtucket formation, including some conglomerates, but princi- 

 pally sandstones and shales, often of reddish-green color, 

 Bellingham series. 

 Green schists. 

 Conglomerates, greatly sheared. 



«Bull. Mus. Comp. Zool. Harvard Univ. No. 16, 1893, pp. 185-225. 



