Section IV., 1894. [ 21 ] Trans. Roy. Soc. Canada. 



II. — The Potsdain and Oalci/erou.s Formations of Queher- and Eastern Ontario. 



By R. W. Ells, LL.D., F.G.S.A. 



(Read May 25, 1894.) 



Ill the volume stj'led " Correlation Papers " (Cambrian) lately issued by Mr. C. D. 

 Walcott, of the U. S. Geological Survey, the author, while reviewing very ably and exhaus- 

 tively, the entire literature pertaining to the subject, states that there are several problems 

 in connection therewith as yet unsolved. Among others of greater or less importance is the 

 limitation of the Cambrian and Cambro-Silurian (Ordovieian) systems, concerning which the 

 geologists who have studied the question from time to time have expressed opinions which 

 differ widely as to the interpretation of the evidence presented in the field. The divergence 

 of opinion is doubtless, to some extent, due to the various standpoints from which the 

 writers on the subject have viewed the question, whether relating to the geological sequence 

 of the formations involved or their palaeontological affinities. To some extent also the older 

 determinations regarding stratigraphy, made in the earlier days of the studj^ of geological 

 science in America, have had some weight in deciding opinion on this question ; 

 and even at the present day we find certain divisions of rocks which difler verj' widely, both 

 as regards stratigrapliical sequence, physical features and fossil contents, placed in the same 

 series, through an intricate admixture of strata due to faults, overturns or other physical 

 disarrangements, which have affected to a greater or less extent, portions of the rocky crust. 



In Canaila some of the most confusing problems in stratigraphy have been disposed of 

 in a tolerably satisfactory manner, both as regards the sequence of strata and the apparently 

 conflicting evidence of the contained fossils and the exceedingly discordant assemblage of 

 facts have been harmonized. These problems are not confined to any particular [iroviuce or 

 group of strata, but have been found as prolific of matter for CDutrover-s}- on the Pacific 

 slope as in the eastern portion of the Dominion. 



In the consideration of the relations of the Potsdam and Calciferous to the Cambrian or 

 Cambro-Siluriau systems, we must bear in mind this fact, that the former of these terms, the 

 Potsdam, does not at the present day possess the same broad significance as when it was 

 employed in the earlier stages of geological investigation. Thus in most of the text books 

 on the subject, in fact until quite recent times, we find that the Potsdam was regarded as 

 following directly upon the Laurentian and Huronian which represented the great Azoic 

 systems. This formation was therefore made to comprise all the rocks of the Cambrian 

 sj'stem. Within recent years however the investigations on the Cambrian by Matthew, 

 Walcott and others have led to a very radical change in the nomenclature, and the rocks of 

 the system which comprise some thousands of feet of slates, sandstone or quartzite and lime- 



