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sheet so that its matrix is often changed to micropegmatite, 

 and but for the vaguely edged boulders it would not be 

 recognized as sedimentary. Often, too, there have been 

 shearing motions giving a schistose structure to the con- 

 glomerate, which has even been mapped as Laurentian. 



The conglomerate passes gradually into the Onaping tuff, 

 which is well displayed at the beautiful falls of Onaping 

 river, where there is a descent of one hundred feet over 



Anticline of Chelmsford sandstone, near Chelmsford. 



these rocks. The tuff is formed of sharp-angled glass frag- 

 ments cemented by volcanic dust, and now transformed into 

 chalcedony, serpentine, etc. It may be called a vitrophyre 

 tuff, as suggested by Dr. Bonney, who first described it. 



There is no distinct boundary between the tuff and the 

 Onwatin slate, which is black and highly carbonaceous, 

 sometimes containing ten per cent, of carbon. In it are 

 found the curious veins of Anthraxolite (anthracitic carbon) 

 which have aroused vain hopes of the discovery of coal. 

 The anthraxolite, which when pure, contains 95 per cent. 



