ALGONKIAlSr EOCKS OF STURGEON RIVEE TONGUE. 475 



instances the scMstosity may be seen to meet the bedding at a very acute 

 angle. In this case the pebbles are usually an-anged with their longer axes 

 parallel to the schistosity, though there are always present a large number 

 that lie parallel to the bedding planes. 



In the least schistose phases of the rocks the pebbles are nearly rotind 

 and the matrix possesses a well-defined fragmental texture, but in those 

 beds in which the schistosity is more pronounced the matrix is sericitic and 

 the pebbles are lenticular. The most completely schistose phases resemble 

 augen-gneisses. In these the matrix is an almost typical sericite-schist. 

 The quartz pebbles have been crushed and flattened into long naiTow 

 stringers or plates of quartz, some of which are continuous for long distances 

 (6 or 7 inches), while others are broken into separate pai-ts, which when 

 rounded on their edges yield quartz lerses like the "augen" of so many 

 augen-gneisses.^ 



The nonconglomeratic beds interstratified with the conglomerates are 

 usually more completely schistose than the latter. The least schistose beds 

 are arkoses. These often show ripple inarking and current bedding. As 

 the schistosity increases, the quantity of sericite present also increases, until 

 in the most highly schistose phases seiicite-schists result. 



Some of the arkoses, as well as some of the finer-grained conglomerates, 

 in addition to being schistose, are also foliated — i. e., they are built up of 

 plates or leaves, along the planes between which they split very easily. 

 When this is the case, the cleavage surfaces are covered by small scales of 

 silvery mica. The foliation is so pronounced in many cases that the rocks 

 are almost fissile. 



Besides these rocks there are jDresent near the dam great ledges of 

 coarse and fine grained greenstone (see PI. LII), whose relations to the 

 sedimentary beds at first glance appear to be those of interleaved flows. 

 Upon close inspection some of these masses disclose intrusive features. 

 Although they almost invariably follow the bedding of the fragmental 

 rocks, some of the greenstones can be seen to cut across the layers in such 

 a manner as to leave no doubt of their intrusive character. 



' The T)e8t examples of these extremely schistose conglomerates are not found in the exposures 

 referred to above, but they are well developed along the line between sees. 11 and 12, T. 42 ^f., R. 29 W. 

 Here the width of the series is but one-fourth mile, whereas the total width of these rocks and tbeir 

 associated greenstones near the dam measures a full mile. 



