﻿228 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 9, 



states of preservation, — from a nearly sound state to a condition re- 

 sembling calcination. They are most commonly composed of loosely 

 cohering layers of soft calcareous matter, of a bright pearly lustre ; 

 and are therefore extremely fragile. Both valves are often in contact, 

 and are filled with smaller shells and sand ; but the majority are 

 broken into small fragments, or have even fallen into a white powder. 

 The small shells just spoken of are Planorbes, Physce, Lymncece, 

 Melanice, Paludince, &c, and are particularly abundant in a living 

 state in the river Notawasaga ; and thousands, like those buried in 

 the sand, are lying dead on the strand about the mouth of the river. 



While the TJniones occur by themselves, squeezed together en 

 masse, a great number of the others are scattered about in the sandy 

 layers around. 



These two remarkable seams of shells are very distinct for three 

 miles downwards, and are from time to time visible nearly to Lake 

 Huron. They extend most probably a considerable distance from 

 the river laterally. The lofty bank in which the shells occur is mi- 

 nutely stratified. Above, it is composed of coarse brown sand, with 

 very thin sprinklings of gravel, and in one spot, at about mid-height, 

 three contiguous layers of small pebbles occur ; — below, it consists of 

 very white and fine sand, which rests upon white clay, mixed with 

 pebbles, similar to those in the sand. This clay, or marl-clay, forms 

 the river-bottom ; it has a fine texture, and breaks conchoidally, or 

 crumbles. In one place it is 20 feet thick above the level of the 

 river. 



Of the very extensive south coast of Lake Huron I only know what 

 may be gathered from a coasting-voyage, and from landing at two 

 or three spots, as at Presqu'isle and in Thunder Bay, where I found 

 erratics of trap and jasper-pudding-stone, and native slabs of lime- 

 stone, — derived from the N. 



The main shore is everywhere low ; the beaches are sandy, but the 

 points are either faced with broken ledges of limestone, or with nu- 

 merous erratics. 



River St. Clair, Lake St. Clair, and River Detroit. — I now quit 

 Lake Huron for the Rives St. Clair ; of which, for want of fuller 

 notes, I have only to say, that its larger detritus is from the north 

 shores of Lake Huron. 



Lake St. Clair, being in a marshy country, shows very little detri- 

 tus, and this on its south shore, where the few small stones that are 

 to be seen have been derived from Lake Huron. I particularly re- 

 marked the handsome greenstone-porphyry of its north shore. 



In the river Detroit, the gneiss, granite, and trap of Lake Huron 

 are plentiful, but not large. The clay of the banks of this river con- 

 tains freshwater shells ; — a fact of considerable importance*. 



Lake Erie and River Niagara. — Lake Erie is situated in the lowest 

 depression of the great level south of Lake Huron and west of Lake 

 Ontario. 



As this vast tract of low undulating ground is overspread with 

 great sheets of blue and red clays, having sands above them, so we 

 * Mather, Silliman's Journal, vol. xlvii. p. 261. 



