﻿F7'oblems in Quebec Geology. 489 



named by Logan, were the equivalents of the Shawangunk 

 or Oneida conglomerates of the New York geologists, and 

 lay between tlie Eichelieu shales and Medina sandstone. 

 He also regarded the peculiar rocks of the mountain 

 region as the equivalents of these, their metamorphic and 

 crystalline character being the result of chemical action, 

 so that the fossils could no longer be recognized. The 

 rocks thus metamorphosed were also stated to belong to 

 the Hudson Eiver group and to the Sillery division, and 

 he added that the changes which these sedimentary beds 

 had undergone were often remarkable, some of them 

 passing into chloritic, micaceous and talcose schists, while 

 others took the form of felspathic, hornblendic and epidotic 

 rocks. 



In 1855 Prof. James Hall presented his report on the 

 graptolites of Point Levis, and in this the age of the strata 

 in which these fossils were found was held to be that of 

 the Hudson Eiver formation. Up to 1857, in which year 

 this report was published, there was therefore a great 

 unanimity of opinion as to the comparatively recent age 

 of the several divisions of these strata, though of necessity 

 there were many complex explanations in order to account 

 satisfactorily for the marked differences in character 

 between the various groups, more especially as regarded 

 the crystalline division. The first change of opinion as to 

 their age is due to the researches of E. Billings, who, from 

 an examination of certain fossils collected from the Levis 

 rocks in 1856-57, found among these certain forms, char- 

 acteristic of the Calciferous and Chazy formations as 

 developed in the Ottawa valley, where these strata are 

 undisturbed. In consequence of this discovery Billings 

 came to the conclusion that a great portion of these strata 

 were referable to the base rather than to the summit of 

 the Lower Silurian, as had so long been supposed, and that 

 the Levis and Sillery rocks were in reality older than the 

 Trenton limestone. 



