SOURCE OF ST. PETER's RIVER. 195 



of Terebratulites, Encrinites, and a Madreporite, (Linne :) 

 the ti'ue nature of the last of these could not be ascer- 

 tained without a comparison of characters, which we were 

 unable to make on the spot, and w^hich the loss of all the 

 specimens collected between Fort Wayne and Fort St. 

 Anthony has prevented Mr. Say from making since ; the 

 rock is of a grayish-yellow colour, with a loose structure. 

 We are aware that some of the characters, which we have 

 given of this rock, might lead to the opinion that it resem- 

 bles the mountain or carboniferous limestone of Messrs. 

 Conybeare and Phillips; and consequently that it is the 

 same as the metalliferous limestone of other geologists ; 

 but we would consider this union as a very hasty, not to 

 say, an incorrect one. Although its cavernous nature, its 

 indications of crystallization, and its organic remains, pre- 

 sent an apparent correspondence with those of that lime- 

 stone, as described by the Rev. W. D. Conybeare, in the 

 excellent " Outlines of the Geology of England and 

 Wales," (Part I. p. 353.) we incline to the opinion that 

 this rock is of a much later formation ; we believe it to be 

 connected with a limestone which was subsequently ob- 

 served on the Mississippi, between Prairie du Chien and 

 St. Anthony, and in which we observed an oolite and a pulve- 

 rulent limestone similar to the calcareous ashes described by 

 Mr. Freiesleben in his elaborate account of the formations 

 of Thuringen. If we compare the characters of this rock 

 with those of the limestone observed by Mr. Freiesleben, and 

 described by him under the name of zechstein and rauch- 

 7vacke, we will be surprised at the great similarity in their 

 appearance. The " zechstein is a compact, hard and tough 

 limestone of an ash-gray colour passing into blackish-gray, 

 distinctly stratified, without however presenting any slaty 



