Quebec Group of Logan. 139 



In this connection it may be proper to adduce even the 

 commonplace consideration of personal convenience in 

 favour of the use of the term Quebec series. In collecting 

 fossils or observing physical phenomena on the Lower St. 

 Lawrence, it may often be impossible to assign a particular 

 band of shale or boulder conglomerate to any special 

 horizon in the chazy or calciferous. yet it can be referred 

 safely to Logan's series. For example, the shale at Metis, 

 containing the remarkable sponges lately described, 1 may 

 be an equivalent of the Levis shale, or a little lower, and 

 ma} T be contemporaneous with Upper Calciferous or Lower 

 Chazy ; but all that can be positively affirmed at present is, 

 that it is in the Quebec series. 



For such reasons as the above, I have retained the name 

 " Quebec Series," in my recently published handbook, as 

 the name for the Atlantic type of the lower member of the 

 Ordovician, and as equivalent to Upper Calciferous and 

 Chazy of the interior region of America. I would com- 

 mend this view of the matter to other geologists, in con- 

 nection with the principle stated above, of the utility of 

 local names for local developments of particular series, 

 while the great systems of formations should have general 

 names. 



It may be said that the same arguments would necessi- 

 tate the retention of the Taconic system of Emmons. To 

 this I have not the slightest objection, provided that the 

 same rule be applied to it ; namely, that it be taken on 

 Emmons' own definition, and without including rocks or 

 fossils referred by mistake, either by him or by others, to 

 the horizon so defined. 



In his American Geology, 1855, Emmons says (part II. 

 p. 6) that in 1836 he had regarded the Potsdam sandstone 

 as " the base of the Silurian system," but that he had since 

 found " the same base resting on sediments still older." 

 These he called the Taconic system, and defines this as a 

 fossiliferous group under the Potsdam, and itself " found to 



1 Trans. Roj al Soc. of Canada, 1889. 



