1896.] MICROSCOPICAL JOURNAL. 229 



had sufficient previous experience or who may be on the 

 verge of entering* into this class of investigation so that 

 they may readily overcome the difficulties ordinarily 

 offering in such cases. 



In the first decade of my study the numerous samples 

 or specimens of diatom-bearing clays which passed 

 through my hands were treated, and acceptable results 

 were obtained, by the universally known methods of 

 washing in water and treatment in acids, concentration, 

 etc. In my later experience I have struck deposits of 

 such a character that it was impracticable, or even im- 

 possible to reduce or eliminate the clay matrices so as to 

 get a rich concentration of the contained fossil organisms 

 by any acid form of treatment. I then devised the 

 method of clay elimination by the trituration or rubbing 

 method, which gives unvarying results so far as relates 

 to the fossil contents of any clays thus far examined. In 

 an attempt to outline the method, it will be necessary at 

 the outset to mention a few requisites essential to the 

 process. The first requisite is to provide a piece of 

 rather stiff rubber belting, having the dimensions of 

 from six to nine inches in length, by some five or six 

 inches in width. Eventually all samples of clay to be 

 treated are laid thereon as a support. 



The preliminary step in the cleaning is begun by tak- 

 ing a small piece of the material, of about a half cubic 

 inch in bulk or smaller, wetting, softening and breaking 

 it down in a small quantity of water to a pasty condition, 

 which will partially liberate the heavier sediments and 

 retain in suspension the clayey or lighter portions. The 

 vessel in which this is done (say a common china soap 

 bowl) is then filled up with water and the lighter portion 

 gradually poured off, retaining the heavier sediment; 

 the initial pressures used in breaking down the clay are 

 in the thumb and finger-tips of the hand and afterwards 

 the ball of the thumb is used in triturating the clay on 



