i62 Transactions of the Canadian Institute. [Vol. V'II. 



The area had thus taken part in three great cycles of deposition 

 concomitant with three great continental oscillations, or a long continued 

 single oscillation of varying rate. During two of the cycles great lime- 

 stone deposits were made within its boundaries. The nearest known 

 areas of Lower Carboniferous are in Michigan, 140 miles away, and their 

 composition is such that it is usually inferred that ever since the close 

 of the Devonian period this area has been above sea level and exposed 

 to denudation and dissection. 



POST-CARBONIFEROUS HISTORY. 



Mesozoic, Cainozoic and Early Pleistocene Epochs. — There 

 is little or no direct evidence of the history of the area during Carboni- 

 ferous and Mesozoic time. The late Mesozoic was a period of extensive 

 peneplanation throughout most of North America. In Wisconsin and 

 Michigan to the west, and in New York and Pennsylvania to the south, 

 the remnants of the planation surface have been recognized. It seems 

 probable that the same planation processes, working northward from 

 these areas, and southward from the Arctic region, may have, in part, 

 produced the younger of the two plains upon the Archean areas in 

 Canada. It is true, this plain may be of pre- Palaeozoic age. Whether 

 it is such, and yet younger than that beneath the sediments cannot be 

 shown until it is proven that the sediments once actually rested upon it, 

 and not upon a surface now eroded awa)% This latter would be the 

 former northward extension upon which they now rest (figure i, BF 

 p. 144). The study of the isolated outliers, such as those of the small 

 areas of limestone in the Lake Nipissing region and elsewhere, may 

 show that they are preserved because thrown into their present protected 

 positions by the downthrow of a fault block. If so, the probability of 

 this plain being of Cretaceous age will be strengthened. By way of 

 comparison it may be noted that a series of faults dislocated the early 

 sedimentary rocks of Sweden and Norway. Later planation left only 

 a few small patches at baselevel, upon the downthrown blocks. Subse- 

 quent elevation of the whole area, and erosion of these softer remnants 

 produced a series of depressions, in some of which are still found isolated 

 patches of the soft rocks. The lower portions of these depressions 

 frequently form lake basins, the most noted of which are Boren, Roxen, 

 Glan, and Braviken. 



The period of Cretaceous planation was followed by an undetermined 

 amount of elevation of portions of the continent, probably including this 

 area. The immediate effect of such an uplift would be the active 



