194 Dr. BiGSBY ow the Geography/ and Geologi/ of Lake Huron. 



in it? association with gypsum^ is closely allied to the red marl of English geo- 

 logistSj and to the old red sandstone of Werner ; and in these particulars it 

 agrees with the sandstone of the Genesee, in the state of New York, pro- 

 nounced to be the old red sandstone of Werner by the very eminent Maclure. 



Connected probably with the horizontal sandstone are the calcareous rocks 

 of the island of Michilimackinac. Their character is well developed at the end 

 of the north-east cliff, adjacent to the fort. At the top of the cliff a few hori- 

 zontal strata, very thin, white, and soft, appear : but immediately below, the 

 limestone loses the appearance of stratification, and becomes yellow and 

 rag-g-ed. The texture of much of it is compact ; but it is more usually vesi- 

 cular (as if from bubbles of air), the sides of the vesicles being encrusted 

 with crystals of quartz, in botryoidal clusters. A few of these vesicles are 

 3 or 4 feet in diameter, and contain several series of smaller cavities. About 

 the middle of the western side of the island there is a cave, about 7 feet deep, 

 formed by the confluence of several of these bowl-shaped hollows or vesicles, 

 whose interior is here also subdivided into smaller cavities. 



Other parts of the limestone, contiguous to the vesicular, are an aggregate 

 of short angular fragments of slaty limestone and broken flints, in the greatest 

 disorder, the interstices being empty, and hned with quartzose crystaUizations. 

 The fragments are from 1 to 8 inches in diameter, and they also are of an 

 ochry yellow colour. The vesicular limestone and the breccia are nearly equal 

 in quantity. 



The bottom of the cliff consists of horizontal and moderately thick strata of 

 limestone-slate, of a white or blueish-white colour, very soft — so much so as 

 even to write. In some parts of the island the limestone contains a few blue 

 and white striped flints. The limestone-slate forms the floor of the lake for 

 miles around, and in some part of the island or other may be found at every 

 level. After a careful search, I met with no organic remains in this limestone. 

 A friend met with a single bivalve, which may have come, however, from a 

 distance, as I observed on the isle several loose fragments, bearing the inci- 

 sions observed in the limestone of the Little Manitou. 



The cavernous and brecciated limestone of Michilimackinac seems to be 

 allied to the magnesian breccia, which, at Bristol and in other parts of England, 

 is connected with the red marl. I have stated that this limestone is probably 

 connected with the red horizontal sandstone of Lake George. My reasons 

 for being of this opinion, independent of those founded on the local proximity 

 of the two formations, are, that in all the other lakes, and in Lower Canada, 

 throughout the whole of the valley of the St. Lawrence, in the lake and terri- 

 tory of Michigan, and in the Illinois, similar beds of horizontal sandstone, sup- 



