STATE GEOLOGIST. 51 



At several points on the south shore of the island, the thick 

 strata above the Pentamcrus beds, appear well calculated for 

 architectural uses. The rock is highly crystalline, hard and 

 white, with occasional stripes and blotches of a rose color, and 

 can be conveniently procured in blocks of any required size. 

 It is not at all unlikely that quarries may be opened which will 

 furnish a stone sufficiently homogeneous to be used for orna- 

 mental purposes. For rough, substantial masonry, there is no 

 rock in our State which is more worthy of attention; and when 

 once developed, there will be no building stone of equal excel- 

 lence half as accessible to our people. 



This group of rocks occupies the southern portion of the 

 Manitoulin chain of islands to the east and south cast of Drum- 

 mond's, underlying the peninsula between Georgian Bay and 

 Lake Huron, and stretching thence to Hamilton, in Canada 

 West, crossing the Niagara river between Grand Island and 

 Lake Ontario, and forming at Lockport, in New York, the quarry 

 stone which has been sent a thousand miles to build the steps 

 at the St. Mary's Ship Canal. 



Toward the west the Niagara Group occupies the whole 

 6hore as far as Point Detour of Lake Michigan, except the 

 promontory, west of Mackinac. Continuing south-west, it 

 forms the Potawotomie Islands, and the peninsula between 

 Green Bay and Lake Michigan, the coast of which it does not 

 leave until it reaches the neighborhood of Evanston, near Chi- 

 cago. 



T. — Onondaga Salt Group. 



On the east side of Little St. Martin's Island, north of Mack- 

 inac, is seen at the surface of the water a mass of gypseous 

 mottled clay, constituting the lowest beds of the Onondaga Salt 

 Group of New York. On the main land west of Mackinac the 

 clays again appear, and in the vicinity of Little Pt. aux Chenc 

 they are seen inclosing numerous masses of aggregated crys- 

 tals of brown and gray gypsum. From the latter locality sev- 

 eral ship loads wore at one time sent off, bu^ the business was 



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