ABSTRACTS OF PAPERS 



59 



MIGR08C0PIG 8ECTI0^'8 OF TILL AND STRATIFIED CLAY 

 BY ROBERT W. SAYLES 



To grind microscopic sections of tillite and slate is a simple matter, but to 

 obtain good sections of till and stratified clay in which the grains have not 

 been disturbed since deposition is more difiicult. For a long time I have been 

 especially desirous of having thin sections of till and clay to compare with 

 sections of tillite and slate. Heretofore the only method of comparing season- 

 ally deposited slate layers with similar clay layers has been by taking small 

 amounts of material from the coarse and fine parts of the yearly components 

 and examining the grain under a microscope. Of the actual structure of the 

 rock particles and their attitudes in the layers, nothing could be known except 

 what could be seen with a low-power glass. Berkey was able to study the 

 layers in the Grantsburg clays in this manner and obtain very Important re- 

 sults, for this deposit lent itself to this crude method. 



Figure 1. — Section of Clay, Woodsrille, Xew Hampshiie 



After many attempts and failures to obtain a satisfactory microscopic sec- 

 tion last year, I sought the advice of my friend and colleague, Prof. E. C. 

 Jeffrey, of the Botanical Department of Harvard University. Through his 

 help, after. several unsuccessful experiments, a method was devised by means 

 of which sections have been ground without disturbing the grains, although 

 it has been impossible to avoid altogether cracks in the coarser clays. 



The method of preparing the till or clay specimens for grinding is as fol- 

 lows: The material must be perfectly dried in a warm bath from seventy to 

 one hundred degrees centigrade. Cool and drop into chloroform in a wide- 

 mouthed l)ottle. Exhaust air to the extent of one atmosphere by high vacuum 

 air pump used for several hours, so as to bring about complete penetration of 



