LAKE ERIE. 61 



Point Pele island, Bolton's island, 



Middle island. Hen and chickens, 



Strontian island, Turkey island, 



Snake island, Cedar island, 



Besides, many islets, when the lake is low. 



All these islands are west of the line, which separates the 

 sandstone from the limestone formation, — so they are either 

 underlaid with the latter rock, or some of its kindred miner- 

 als. Some of them contain beautiful sulphate of lime, or 

 crystaline gypsum. 



One island contains so much sulphate of Strontian, as to 

 give the whole island the name ft bears. In the summer of 

 1828, while in that region, we procured hundreds of specimens 

 of this mineral, which we brought home, and now describe 

 them, as they lie before us. They occur both massive and 

 regularly crystalized. The crystals are usually four-sided 

 prisms, variously modified, and terminated by two, four or 

 eight sided summits, sometimes compressed into tables. 



Its most common form, is an oblique four-sided prism, ter- 

 minated at both ends, by four faces, standing on the edges, at 

 the sides. The crystals are frequently long and slender, col- 

 lected into fascicular groups, whoso faces have a strong lustre, 

 but are not transparent, though translucent. Its fracture is 

 foliated and glistening; — its color varies, but is either, bluish, 

 milk-white, gray or reddish. 



Strontian island, is about twenty miles from Sandusky City, 

 and is well worth visiting, by the mineralogist. This lake 

 rises seven feet higher in some years than in others, so that 

 islands one year may be covered with water the next. We 

 have said many of these islands contain gypsnm, but, that 

 mineral is found in great abundance under the waters of San- 

 dusky bay, and on the point of land which lies between that 

 bay and the lake. This is a granular gypsum, crystalized, 

 and beautifully variegated by streaks of blue, red and white. 

 Large quanties of this gypsum are dug and carried away, 

 down our canal, as far as Muskingum county. It is used as 

 a cement and as a manure, or stimulant for vegetables; for 



