CORROSIVE ACTION OF BRINES IN MANITOBA 



463 



phere; and the writer believes that it is primarily as an agent for 

 distributing the liquid in a thin film over the bowlder, and only 

 secondarily as a direct chemical agent, that the dissolved material 

 in the brine acts in the process of disintegrating the bowlder. It 

 has been proved conclusively that water is itself an agent of con- 

 siderable chemical power and that it acts most vigorously as a 



Fig. 2. — Corroded bowlder, salt flat, Pelican Bay, Lake Winnipegosis 



corrosive agent when in intimate contact with the atmosphere, 

 as, for instance, at a water surface. 



The actual process of disintegration is necessarily different for 

 different minerals. The ferromagnesians, more particularly the 

 amphiboles and pyroxenes, have suffered to a greater extent than 

 the feldspars. The alkaline earths are somewhat readily attacked 

 and dissolved as carbonates or chlorides, and silica with alumina, 

 mixed or combined, is left in colloidal form. The percentage of 

 soluble material in the case of the feldspars is correspondingly 

 smaller. To some extent, with the metasilicates at least, the 



