General Description of Lake Erie. 381 



O upon P, 128° 31'— of O upon o, 77° 2— of O upon the 

 returning face, 102° 58'— of d upon d, 101° 32'. 



SI 



Another is, '♦ Sulphate of strontian epointee MAEP" (fig. 



III). It is " the former, having the soHd angles deeply trun- 

 cated, forming faces parallel to the sides of the primitive rhom- 

 boidal prism. The inclination of M upon M is 104° 48' ;— that 

 of the other faces coincides with the inclinations of the * trape- 

 zienne.* The crystals are translucent in a great degree, ap- 

 proaching to transparent, and of a bluish-white colour. The 

 size of the crystals is large. I have seen fragments belonging 

 to crystals which must have been four or five inches long, be- 

 longing to the sub-variety ' trapezienne elargie.' The surfaces 

 of the faces oo are usually dull, of a more opaque milky white 

 than the remainder of the faces, which have a remarkably fine 

 lustre ; the faces corresponding with those of the primitive 

 rhomboidal prism, as P and M, display a fine iridescent 

 colour." 



The strontian of the Miami river occurs at Fort Meigs, and 

 was first made known by Mr. Schoolcraft. I am not aware of 

 any account of this locality having yet been published. The 

 crystals Mr. Schoolcraft showed me are precisely the same as 

 the smaller of those in the cavity at Moss Island in Lake Erie. 

 In Celeron and Grosse Islands it is found in small balls and 

 geodes ; at the former in confused crystalline masses — at the 

 latter, it lines cavities in crystals seldom exceeding an inch and 

 a half in length, and terminating by a lanciform opaque white 

 point, more or less disintegrated. Their colour is a fine sky- 

 blue, and their lustre and transparency are considerable. The 

 strontian is only sparingly scattered through this limestone. It 

 is best characterised and most plentiful in a quarry at the lower 

 end of Grosse Island. The reefs of rock, crossing the river 

 Detroit above the adjacent island of Boisblanc, show faint 

 traces of strontian. It is remarkable that wherever there are 

 organic remains there is no strontian, and vice versa ; but this 

 only applies to Lake Erie and its vicinity — for the limestones 

 of Lakes Huron and Simcoe exhibit both together in the same 

 hand-specimen. 



All that is known of the fixed rocks of Lake Erie, I believe 

 I have now stated. It remains to be mentioned that on its 



OCT.— DKC. 1828. 2 D 



