128 Canadian Record of Science. 



fossils. Still it would be obviously incorrect to say that 

 the two sandstones were of the same age. This would be 

 equally true were each of the beds represented in the 

 figure a series of similar beds, instead of a single one. 



When the exposures are far removed from the oldland 

 shore, and there is very little doubt that the old landward 

 extension of the beds is completely gone, the order of 

 superposition in the cliff, or across country in a region of 

 lightly inclined dips, may be taken as the. order of succes- 

 sion. Such a series as that represented by the Medina- 

 Niagara series in Central Ontario and Western New York 

 will serve as a case in point. In areas adjacent to the 

 margin of the ancient sea the correlation of the widely 

 separated deposits on lithological or even palgeontological 

 grounds must be made with great care. Where lithologi- 

 cally similar deposits carry similar fossils contemporaneity 

 of epoch may generally be postulated. If, on the con- 

 trary, the forms are not identical, and the deposits are 

 lithologically unlike, they may still be contemporaneous 

 deposits of different zones. 



Where a small exposure of rock is found carrying 

 fossils which are normally considered to be characteristic 

 of two different terranes, and as a consequence the beds 

 are inferred to be transitional ones between the two 

 terranes, it must also be recognized that this portion of 

 the bed may mark a transition in a horizontal direction, 

 being but a portion of a synchronous bed of varying 

 members. 



Applying these considerations to the correlation of the 

 sedimentary deposits along the margin of the Frontenac 

 axis, so far as the writer is aware, no single bed has been 

 traced through various zones. Whether it is possible to 

 do this is problematical, because of the discontinuity of 

 the outcrops. Inasmuch as this has not been done, there 

 must be a factor of uncertainty in any conclusions which 

 may be reached. There remains, however, the question 

 as to what interpretation does the balance of probabilities 



