264 On the Oeography and Geology 



lake at the present day, but much thicker, and, of course, heavier. 

 They arc onp or two feet apart, and are buried under 150 feet of 

 sand, in various degrees of preservation ; from being nearly sound, 

 to a state of pulverulence resembling calcination. They, most 

 commonly, are composed of loosely-cohering layers of soft calca- 

 reous matter, with a very bright pearly lustre ; and, therefore, are 

 very fragile. Both valves are often in undisturbed contact, having 

 the interior filled with small shells and sand ; but many are 

 broken into small fragments and disseminated in white pow- 

 der through the containing sand. They are never fossilized. 

 The smaller shells alluded to are Planorbes, Physae, Lymnaei, 

 Melanise, and Paludinae*, which are particularly abundant in 

 Notawasaga Bay in a living state. While the alismadontae are 

 compressed into layers, these are scattered for a small distance 

 through the neighbouring sand. They are occasional in a loose 

 state on the banks and bed of the river from near its north source 

 to the mouth. 



The occurrence of fresh-water shells in the great alluvial beds 

 on the east of Lake Huron, appears to argue them to be a post- 

 diluvian operation ; effected while the waters were still of immense 

 height and extent ; — and the idea is confirmed by the fact, that 

 in Lake Superior, the materials of similar deposits, in most cases, 

 belong indisputably to the vicinity in which they occur ; as at 

 Huggewong near Montreal River, where the rounded masses of 

 the sand-bank are of the white granite of the place; as at the 

 head of the River St. Mary, where the sands have the ferruginous 

 tint of the red sandstone on which they repose ; and as the Black 

 River where the gravel consists of the greenstone, pale red granite 

 and quartzy matters of the district. 



In addition to the movements in these great collections of waters 

 arising from storms, lunar attractions, aad sudden drainage, or any 

 other cause, a powerful agent in breaking up and removing rocks, 



♦ Precisely the same shells exist in a marl bed, laid open in the summer 

 of 1823, by the cutting of La China Canal, near Montreal, in Lower Canada. 



