in some oj our Tost Tertiary Deposits. 49 



derable height above the level of the lake may be attributable to a gra- 

 dual elevation of the land or to a subsidence of the water. The last 

 hypothesis seems the most tenable, since the first would involve a local 

 upheaval only, and an inclination of the plane of the terraces at variance 

 with their apparent horizontality. Should further researches prove the 

 existence of terraces or other indications of old beaches on the western 

 margin of Lake Huron corresponding in height with those discovered 

 along the eastern shore, the supposition that the level of the water has been 

 lowered by the wearing away of some barriei' will be strongly supported ; 

 and if this be allowed as a reasonable explanation for these geological 

 monuments, we have then, by drawing contour lines coinciding with 

 their level the means of discovering the probable position of this barrier. 

 From all that I can learn regarding the relative levels of the country 

 these lines would pass over the peninsula between Lakes Huron and 

 Erie at some distance inland from the River St. Clair and would if 

 continued eastward along the shores of Lake Erie fall within the summit 

 of the neck of land through which the chasm of the Niagara Eiver is 

 cut." 



The northern part of the Township of Nottawasaga is situated on 

 the extensive sandy plain above aUuded to, which was no doubt for- 

 merly covered by an extension of Georgian Bay to the south-east- 

 ward. The whole has a general slope up from the bay, but here and 

 there a ridge of gravel or coarser sand interrupts its general uni- 

 form aspect. Hurontario Street, running from Collingwood Har- 

 bour almost due south through the township, was carefully lev- 

 elled by Wm. Gibbard, C. E., and it appears from his profile 

 section of the street, that from Collingwood to the north side of 

 the Pretty River at the Village of Melville or Nottawa Mills, a 

 distance of two and a half miles, the ground rises very regularly 

 from the edge of the water to an elevation of 138 feet, or at the 

 rate of about 55 feet per mile. At the Pretty River a change 

 begins both in the character of the surface and in the rate of its 

 inclination, which continues regularly for three and a half miles fur- 

 ther at 4*7 feet per mile. Thus, at a distance of six miles from the 

 present shore, the surface has attained an elevation of more than 

 300 feet above the level of the lake ; beyond this it rises irregu- 

 larly and much more rapidly. It is evident that the bank of sand 

 and gravel on the north side of the Pretty River continued for a 

 longtime to be the shore of the lake. The layers of sand and gra- 

 vel are arranged exactly as on a modern beach, and among them I 

 noticed several thin irregular beds of a light grey or white colour, 

 composed principally of carbonate of lime. In the cutting 

 through the top of this ridge the common land shells Helix al- 



Can. Nat. 4 Vol. VI. 



