MUSEUM OF COMrAIlATIVE ZOOLOGY. 65 



rock may be so changed as to be taken by observers for a sedimentary 

 stratified one, even a good dolomitic limestone. The origin of the ser- 

 pentinous part by direct change in situ of a peridotite (eruptive), as well 

 as by the tilling of tissurcs in the peridotite by serpentinous material 

 derived from the surrouxiding rock, would seem in the main to be 

 consonant with the observations of Bonney, Becke, Berwerth, Dathe, 

 Doelter, Drasche, Hochstettcr, Koch, Lemberg, Sandberger, Streng, 

 Tschermak, Zirkel, and others. Peridotite, which we provisionally 

 classed with gabbro under basalt, in a preliminary publication " On the 

 Classification of Rocks,"* it would seem from further and more extended 

 study, should be classed as a distinct species ; and some other rocks 

 may possibly belong with it. This species would represent a more basic 

 one than basalt, containing generally between thirty-five and forty-five 

 per cent of silica, or, more nearly, forty to fort^'-three per cent. The 

 reasons for this view it is intended to give fully in another publication, 

 but they would be out of place here. 



The following analyses (incomplete) of this peridotite were made and 

 published by Prof. Whitney : — 



IV. 



SiOz 

 AI2O3 



^^^^^ ) o- -. 6.75 12.90 



34.50 16.50 



FeO ) 14.14 19.52 



MgO 14.83 33.07 28.67 14.83 



CaO 



Na20 



H2O 



100.00 98.86 



Analysis I. is taken from Foster and Whitney's Report on the Geology 

 of Lake Superior, II. 92. Analyses II., III., and IV., from the Ameri- 

 can Journal of Science, (2,) XXVIII. 18. 



Three miles and a half northwest of Ishpeming, or one mile and a half 

 west of Deer Lake, serpentine occurs abundently on the land of Mr. 

 Julius Ropes, postmaster of Ishpeming.t This rock, although quite 

 hard, forms very beautiful specimens when polished (234, 235, 236, 237, 



* Bull. Mus. Comp. Zo61o£n,r^ y. 279. 



t First Annual Eeport of the Commissioner of Mineral Statistics of the State of 

 Michigan, pp. 204-206. 



VOL. VII. — NO. 1. 5 



