1896.] MICROSCOPICAL JOURNAL. 231 



of the bowl. A stage will then have been reached 

 where no further pouring in or off of water will be re- 

 quired. The results up to this point have eliminated all 

 of the undesired clay or aluminous products and left be- 

 hind the desired organic fossils, largely mixed with sand 

 grains. Since this last condition is somewhat objection- 

 able, it then becomes necessary by some concentration 

 process to remove the desired fossils from the sand as 

 fully as possible. This need then causes one to resort to 

 the concentration method customary in removing the 

 diatoms from recent fresh water and marine muds or 

 clays. This procedure is familiar to everyone who has 

 given any attention to the cleaning of diatoms. To con- 

 duct thisconcentration successfully it is usually necessary 

 to have relatively shallow dishlike vessels of glass or 

 porcelain, of either sc^uare or round contours. Square is 

 preferable, as the concentrated particles may be directed 

 to a corner and drawn off by tip of index finger contact, 

 or with a pippette. When this is successfully done the 

 objectionable sand is left towards the rear of the 

 diatoms, spiculfe, etc., and may be rejected as practically 

 barren of forms. 



The manipulation properly conducted, should be that 

 form of motion, comprised in a continuous twirling 

 motion of the contents of the glass, while holding the 

 glass slightly slanting, and giving it an occasional jerk 

 backwards, so as to project the discoidal and other forms 

 forward. This method used with the marine clays 

 drives millions of the diatoms forward and out of the 

 sandy sediment, but also carries with it all of the 

 vegetable debris usually burned out or carbonized during 

 acid treatment. 



At this point it may not be inappropriate to introduce, 

 by way of diversion, an important expedient in the cen- 

 centration of diatoms as devised and utilized by myself, 

 useful in more general cases and of more frequent utility. 



