110 G. D. Hubbard — Colloids in Geologic Problems. 



and of course prevents the roots striking deeply. It can 

 be broken np by deep cultivation, but the soil experts 

 are now of the opinion that treatment with an electrolyte 

 is really better. Aluminum sulphate has been success- 

 fully used in a number of cases. It acts much as the salts 

 do in the sea, by coagulation of the colloidal material into 

 little pellets, large enough so that the water and the air 

 can get among them, and thus prevents their operation 

 as cements. 



In western United States, where most of our irrigation 

 is carried on, there have been discovered in recent years 

 great quantities of aluminum sulphate, and it is believed 

 that a large use of this salt will greatly extend the life 

 of our irrigated soils. 



The subject of colloids in geology is just beginning to 

 attract the attention of men who should be concerned with 

 it. While the chemists have tackled their colloid prob- 

 lems with vigor and enthusiasm the geologists have all 

 but neglected the whole field. There should be many 

 geologists turning their attention seriously to the solution 

 of the great numbers of problems now before us, such as 

 these suggested in this paper, and there should be many 

 more geologists keeping up with the literature that dis- 

 cusses these colloid problems. 



Department of Geology and Geography, 

 Oberlin College, Oberlin, Ohio. 



