GEOLOGY. 213 



during its season of liigli waters. Among tliese materials is 

 the oft-mentioned pumice stone, wliicli is brought down from 

 tlie upper parts of the river. I have ascertained, by a more 

 careful exammation than had probably been given to it pre- 

 viously, that it is not a true pumice, but a semivitreous sub- 

 stance, produced by pseudo-volcanoes, that I shall hereafter 

 describe ; the region of which is laid down upon my map. 



" On the elevated prairies above the bluffs, the * erratic 

 deposite ' again appears ; amongst which I found, for the 

 first time, fragments of quartzite in every respect similar to 

 that of the Red Pipestone Quarry. 



*' Mr. Murchison, in his lately published Memoir, refers to 

 a paper by Mr. Lonsdale on the Devonian system, in which 

 that celebrated palceontologist indicates the principal fossils 

 belonging to it ; referrmg, also, to the species found in Bel- 

 gium and in France, as well as in Devonshire. In this list 

 of six species enumerated as belonging characteristically to 

 the Devonian system, I find stromboles vermicularis, or 

 cyathophyllum vermiculare ; and euomphalus radiatus (Gold). 

 The cyathophyllum vermiculare, it appears, is the only 

 species that is found both in the Devonshire rocks and those 

 of the Boulonnais. Well, now, if we take into account the 

 enormous distance that separates the small gi'oup that I have 

 just described, with its equivalent in France and in England, 

 will It be thought hazarding too much to detach it from the 

 place I had first assigned to it in the lower mountain lime- 

 stone, and bring it down to the Devonian system ? 



" The group to which I am now referring, and wliich is at 

 the base of the rocky banks previously described, is very 

 fossiliferous, and has a great extent ; though I had no occa- 

 sion to give it but a rapid examination. I may be permitted 

 to hope that naturalists more fortunately circumstanced will 

 discover among it otlier characteristics by wliich to complete 



