Reviews 



Kaolin of Indiana. By W. N. Logan, State Geologist. Indiana 

 State Dept. of Conservation, Bull. No. 6, 1920. Pp. 131, pis. 

 43, maps (colored) 7. 



Beds of kaolin occur at several horizons at or near the top of the 

 Mississippian formation in several counties in southwestern Indiana. 

 One important horizon is at the contact between a Chester shale (below) 

 and a Pottsville sandstone (above). All the beds are beneath a sand- 

 stone and above a shale. There has been only a slight commercial 

 development of the deposits to date, in spite of the presence of large 

 quantities of high-grade white clays. The report discusses (i) the 

 physical and chemical properties of Indiana kaolin; (2) its geological 

 conditions of occurrence; (3) its origin; and (4) its uses. It also gives 

 (5) its geographic distribution by counties. 



Dr. Logan's study of the origin of Indiana kaolin has disproved 

 earlier explanations. Laboratory experiments and microscopic exami- 

 nation have shown that this kaolin is due to biochemical action, an 

 origin not before suspected. It was found that under proper conditions 

 in the laboratory, sulphur bacteria secrete kaolin. In nature, sulphur 

 bacteria obtain sulphur from the iron pyrite in the shale. The sulphuric 

 acid which is formed, attacks the aluminum in the shale. The resulting 

 compound reacts with the quartz of the sandstone, and the sulphur is 

 replaced by silica, producing kaolin. 



As kaolin in southern Indiana is being actively formed today by 



sulphur bacteria where the average annual temperature is 50° F., it is 



inferred that the kaolin deposits of the Tuscaloosa, Wilcox, and Lafayette 



formation of southern states were formed under similar temperatures. 



During the glacial epochs, sorne such average temperature doubtless 



occurred in the Gulf states. 



S. S. V. 



470 



