STATE GEOLOGIST. 57 



A; >• \ < ral points on the south Bhore ol the island, tin* thick 



the Pentamerus beds, appeal vreil calculated for 



ritectural uses. The rock is highly crystalline, hard and 



white, with occasional Btripes and blotches of a rose color, abd 



can : urcd in blocks "I' any required BJ 



It is not .»: all unlikely that quarriee may be opened which will 

 furnish a stone sufficiently homogeneous t<> 1"' seed lbs oma» 

 cncntal purpose b. For rough, substantial masonry, there is no 

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

 .. there will be bo building Btone of equal excel- 

 lence half as Le to ..ui people. 



This group of 1 a ;upies the s tuthern portion of the 

 atanitoulin chain of islands to th< i I>rum- 



moad's, underlying the peninsula between Georgian Bay and 

 Lakv Huron, and Btretching thence to Hamilton, in Canada 

 \Y< S jara river 1m , Grand Island and 



Lake Ontario, and forming at bockport, id New York, the quarry 

 t^tone which has been Bent a thou-,... i miles to build the step:-, 

 at the St. Mary's Ship Canal. 



Toward the west the Niagara Group occupies the whole 

 shore 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 Lvanston, near Chi- 

 cago. 



7. — Onondaga Salt Group. 



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

 inac, is seen at the surface of the water a ma-s of ir\ pseous 



tiled claj ating the lowest beds of the Onondaga Salt 



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

 cla; appear, and in the vicinity of Little Pt. aux Chenc 



they are seea inclosing numerous masses of a ted crys- 



tals "f blown and gray gypsUQi From the latter locality 

 eral sic at one time sent off, but the business was 



8 



