MICROSCOPICAL, EXAMINATION OF CI.AY. S29 



hot fire, but gradually hardened. Anything like baking is apt to be 

 destructive of delicate specimens. I have been accustomed to treat at 

 one time enough clay to fill an ordinary pie-dish. 



The clay, when thoroughly dry, should be placed in a large bowl of 

 water, and allowed to remain undisturbed for a few hours. It should 

 then be gently stirred up in the water, and it will be found to disintegrate 

 in a remarkable way. 



After the clay has been stiiTed up in the water, it should be allowed 

 to settle quietly. If it is at all rich in organisms, a fine whitish scum 

 will soon form upon the surface of the water, and must be carefully 

 skimmed off. This first scum is the most valuable of all the treasures 

 the clay can yield. It should be treated by itself, unmixed with baser 

 matter, and placed upon a piece of the finest muslin to permit the water 

 to drain away. A very simple and useful plan is to have a small 

 hollow tin cylinder, and affix the muslin to one end by an elastic 

 band. Through such a cylinder the skimmed water can readily be poured, 

 and the muslin will retain the debris in which the organisms will be 

 found. Muslin is preferable to a sieve, since a fresh piece can be used 

 in dealing with the clay from each locality, and the possibility of any 

 accidental accumulation of old material (such as may take place at the 

 edges of a sieve) is prevented. The mesh should be as fine as will 

 permit the drainage of the moisture. When the muslin, with its light 

 burden, is dry, the contents may be placed upon a slate, and any 

 organisms can be readily picked off. 



The process described should be repeated until no scum will rise. 

 It is possible that when a clay has failed to yield any more " floatings," 

 after a second drying it may produce some. If the clay under examina- 

 tion be scarce, and a siapply not readily obtainable, the water should be 

 poured off as soon as all the " floatings" have been collected. The clay 

 remaining at the bottom of the dish should again be dried, and the scum, 

 if it chance to yield any, again collected. When all the " floatings " have 

 been obtained, the clay itself should be washed. This is effected by 

 pouring water upon it, stirring it, and then, after giving a few moments 

 to permit the heavier material to fall, pouring off the water ; and 

 repeating the process until the fresh water is not at all mudded by the 

 stirring of the material that is left. Abundance of water should be 

 freely used ; and generally a great many separate washings are required, 

 but at last, if the clay has been really dry at the outset, the fine mud 

 will disappear. 



The remaining material will consist of grains of sand and pieces of 

 gravel, together with such organisms as would not float ; and must be 

 di'ied for examination. 



If the method described be carefully pursued, nothing ought to 

 escape except the finely comminuted mud ; and the observer ought to 

 have every organism (the Diatomaceae being of course excepted) preserved 

 either in the " floatings" or the " washings." 



