[matthew] CAMBRIAN FORMATION IN EASTERN CANADA 71 



its base yields typical Cambrian fossils. As the effusive and the red 

 rocks are entirely wanting in this basin and there are conglomerates 

 at the base of the red rocks in the St. John basin, it would seem that 

 the connection between these red rocks and the St. John Group is 

 not so close as in Cape Breton. 



A third basin of Cambrian rocks farther to the northwest, how- 

 ever, repeats the conditions in the St. John basin so far as relates to 

 the basal effusives and red rocks, though the measures of the several 

 divisions of the St. John group itself are thin, as in the valley of the 

 Kennebecasis. 



To Cape Breton we need to turn to get a good knowledge of the 

 faunas which mark that part of Palaeozoic history preceding the 

 deposition of the St. John group. In that island we find effusive 

 rocks everywhere at the base of the Cambrian series. At more than 

 one place these rocks may be seen to rest on schist or granitic rock, 

 and this is softened and decomposed at the base as though it had 

 been subjected to long continued sub-aerial weathering. Yet the 

 older rocks must have been near the sea level, for while in most 

 districts they are underlain by a solid mass of effusive rocks, on Indian 

 brook these rocks are comparatively thin, and on Dugald brook, a 

 branch of that stream, they contain the beds of gray shales that con- 

 tains the few species of Coldbrookian fossils listed on a preceding 

 page. On this brook also is to be found the fullest representation of 

 the Etcheminian faunas. 



The rocks along this stream have yielded quite a variety of the 

 earliest types of Palaeozoic Brachiopods and Ostracods; and although 

 Trilobites appear to be absent from all but the highest assise, there 

 is a sufficiently great variety of forms in the two former classes to 

 distinguish two sub-faunas in this Etchemmician terrane. 



Not only faunally, but also physically a distinction may be 

 noticed between the upper and the lower part of the Etcheminian 

 terrane in Cape Breton, for while both consist largely of volcanic 

 effusives, the upper or later portion is composed of finer sediments 

 and is of a purer grey color; this difference of color and texture is 

 noticeable both in the valley of the Mira river and in the basins border- 

 ing the East bay of the Bras d'Or lake. 



ST. JOHN GROUP. 



DIVISION 1 (ACADIAN). 



In passing from the Etcheminian to the St. John terrane there 

 must have been an important change in the physical conditions of 



