132 Canadian Record of Science. 



three, because formed from the same source, these two 

 which are not synchronous but successive would in the 

 usual practice be correlated. The same would be true if 

 each bed, as shown in the diagram, represented a series of 

 similar beds. 



The writer would then suggest that that there is a 



no 



strong a priori reason for assuming that these beds are 

 contemporaneous with the beds of limestone and argil- 

 laceous shales below the Trenton, and probably synchro- 

 nous with some of them. From the general direction - of 

 the dips there is a remote possibility of some of the more 

 distant outliers to the north being synchronous with the 

 lowest beds of the Trenton, but this cannot be proven. 1 



Naturally the question might be asked, would you make 

 all Potsdam contemporaneous with the lower Trenton ? 

 Certainly not. Potsdam, as a formational name, was 

 introduced to denote a horizon which is supposed to be 

 geologically older than the Trenton and which possesses 

 certain definite types of fossils, and should be limited in 

 its use to horizons where these two relations are proven 

 to hold. The extension of the term to horizons in areas 

 where the relations do not hold is apt only to lead to 

 confusion. At present in Ontario much that has been 

 classed as Potsdam, particularly on lithological grounds, 

 is probably contemporaneous with limestones referred to 

 later horizons now exposed elsewhere. The Potsdam 

 sandstone undoubtedly should merge into limestone 

 horizontally, unless our ideas of the processes of deposition 

 are incorrect. Where the line of division comes in it 

 would be difficult to say. 



1 Wilson, Phys. Geol. Central Ontario. In this paper, on the basis of the above 

 deductions, the writer advanced the views outlined here in more detail. Subsequently 

 Dr. Ami, of the Geological Survey Department, described the Kideau Formation, which 

 is made to include the formations here referred to, but the greater part of which lies 

 to the eant of the Frontenac axis, as being the shoreward extension of theCalciferous 

 and Chazy. Dr. Ami's paper (Geol. Soc. Anier., Rochester, 1902. has not yet come to 

 hand, but the writer understands that the results of his studies on the eastern side of 

 the axis in general confirm the conclusions reached by the writer after a study of the 

 smaller exposures on the west. The latter the writer considers as probabiy the shore- 

 ward extension of the eariy Black Klver rather than the Chazy. 



