Page:Midland naturalist (IA midlandnaturalis01lond).pdf/371
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 stirred 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 of an elastic band. Through such a cylinder the strained 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 he used in dealing with the clay from each locality, and the possibility of any accidental accumulation of old immaterial (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 sill 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 examination be scarce, and « supply not readily obtainable, ihe water should be poured off as soon as all the "floatings" have boon 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 precess 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 dried 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 Diatomaceæ being of course excepted) preserved either in the "floatings" or the "washings."