Dr. BiGSBY on the Geography and Geology of Lake Huron. 201 



Manitou ; but there it is not fetid. Specimens from Cabot's Head^ tlie Flower- 

 pots, and the Fourth Manitou^ resemble the fetid limestone of the Little Ma- 

 nitou : they are darker, coarser, very fetid, and abound in the petrifactions 

 common to this range. 



The fissures and surfaces of the limestone strata of the Little Manitou are 

 marked by singular scarifications, not observed in any other part of Lake Hu- 

 ron. They are narrow and shallow, as if made with a penknife, and occur either 

 singly at hazard, or forming a multitude of parallel incisions, placed together 

 promiscuously. They crowd the surface of the rock and of the various or- 

 ganic remains. Their greatest length is an inch, their ordinary length much 

 less. Sometimes they are only punctures, of triangular, rhomboidal, oblong, 

 or semicircular shape. ♦ 



On the south-western shore of Lake Huron, at Presquisle, the limestone is 

 only seen at the bottom of the harbour, forming a broken pavement, on a level 

 with the waters of the lake. It differs little in appearance from the fetid lime- 

 stone of the Little Manitou, being brown, granular, and tolerably hard ; but 

 I did not ascertain its fetor. It contains the organic remains prevalent in the 

 limestone of the Manitoulines *. 



The limestone of Middle Island resembles that of Presquisle, and is full of 

 organic remains. 



The organic remains of the Manitouline limestone have been collected 

 principally in Drummond, and chiefly through the persevering exertions of 

 Mr. M. White of the Army Medical Staff. This island having been assigned 



* I found at Presquisle a loose fragment of limestone, having the peculiar suture observed in 

 that of Kingston on Lake Ontario. This limestone is subdivided, not only by the horizontal 

 planes which render it schistose, but by other planes which also are horizontal. The upper and 

 lower surfaces of these partitions are covered with a brown or black shining matter. They are 

 extremely rough, from their mutually sending forth innumerable processes of the most irregular 

 shape, protruding from half an inch to 1^ inches, which are received into corresponding depres- 

 sions in the opposite surface. A section of the partition resembles the suture of the human cra- 

 nium: like which, the limestone suture can be taken asunder and replaced without fracture. 



The 11th stratum from above, at the Table Rock of the chasm of Niagara, is intersected 5 or 

 6 times in this manner. This suture has also been observed on Lake Erie, in white granular 

 limestone ; and in Lower Canada, at Point aux Trembles and Point Levi, in brown fetid crystal, 

 line limestone. It has been found also in the river St. Clair, in loose fragments of black fetid cry- 

 stalline limestone. 



At Point Levi, and in several of the strata at the great chasm of Niagara, it is very minute, 

 and leaves the horizontal direction, wandering about in the most fantastic curves. It often ex- 

 tends only to a little distance, and disappears as a very small fissure, coated with a thin black 

 scale. 



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