No. 1.] HOFFMANN — RECENT ANALYSES. 57 



•t'lays of the Fort Pierre group cover the luost extensive area. 

 Springs, the water of which come in contact with the Cretaceous 

 rocks also, doubtless feed the tributaries. The Cretaceous shales 

 tjontain a considerable proportion of disseminated pyrites, 

 which latter when exposed to atmospheric influences undergoes 

 decomposition, ultimately giving rise, in the presence of the 

 calcium carbonate contained in the rocks, to the formation of 

 gypsum, with which mineral — generally in the crystalline form of 

 sclenite — many of the beds are in consequence charged. There 

 are also on this side of the Eed River, several springs impregnated 

 with common salt; these resemble those of the Manitoba Lake 

 district, and are probably like them derived from the underlying- 

 Devonian rocks. Springs of this character are known on the 

 Salt River, south of the Pembina, and it was previously attempted 

 to utilize these as a source of supply of salt. Similar springs 

 are said also to occur on the Scratching River. 



The country drained by the Assiniboine resembles in most 

 points that described as giving rise to the other western tributaries 

 of Red River. By some of the eastern branches of the upper 

 part the Assiniboine, from Riding and Duck Mountains, a certain 

 amount of woodland drainage is derived; but by far the greater 

 part of its tributaries bring to it the drainage of prairie lands 

 with a compartively small rainfall, and in which the saline matter, 

 would therefore be supposed to exist in a more concentrated form. 

 Though a compartively small portion of the total length of the 

 streams can flow in actual contact with^the underlying Cretaceous 

 rocks, there is a reason to believe that in the praire region west 

 of the valley of the Red River, a great part of the drainage of 

 the country passes below the drift deposits along the surface of 

 the underlying rocks, and this being brought very intimately in 

 contact with these rocks would be likely to be influenced by their 

 composition. 



These samples of the waters were collected by Mr. A. S. 

 Cochrane, — at the instance of Dr. R. Bell — on the 2t)th of Oct- 

 ober, 1876: that of the Assiniboine was taken from the centre of 

 the river, about a quarter of a mile above its junction with the 

 Red River ; whilst the water of the latter was taken from the 

 centre of the stream, about a quarter of a mile above where the 

 former flows into it. 



The water of the xVssiniboine, after filtration, had a faint 

 yellowish tinge. The suspended matter, which had a brownish- 



