McClung.] Microscopic Organisms of Upper Cretaceous. 417 



microscopical examinations of the deposits have been made by 

 triturating the substances to a moderately fine powder, and by 

 elutriation, separating the desired forms from the rest. So far 

 as the smaller remains, Coccoliths and Rhabdoliths, are con- 

 cerned, this method is entirely satisfactory, but a few trials of 

 it in search for Foraminifera convinced the writer that it is 

 anything but a desirable process. This much might be inferred 

 from the results obtained by the early investigators who dis- 

 covered the minute Coccoliths and overlooked the large Fo- 

 raminifera. The delicate tests of these creatures are almost 

 invariably broken in the crushing of the specimen, and but little 

 conception of their forms and none of their number can be 

 obtained. 



Evidently the only proper way to study them is in sections, 

 where their form and relation to each other are preserved un- 

 disturbed. Some difficulty arose at first in the preparation of 

 sufficiently thin sections of such a soft and friable substance as 

 the chalk, which becomes a mere paste when rubbed on the 

 stone with water. As a means of overcoming this obstacle, in- 

 filtration with shellac was tried, and proved all that could be 

 desired. Fragments of the substances were ground or pared 

 down to the required size, and the tablets thus formed were 

 allowed to absorb all of an alcoholic solution of shellac that 

 they would take up, and were then baked in an oven until dry. 

 Thus prepared, they were quite hard and tough, and submitted 

 readily to grinding upon a stone, or upon a glass plate charged 

 with fine emery powder and water. 



Two or three hours usually suffices to drive off the alcohol 

 from the shellac, and then the specimens are ready to be re- 

 duced to sections. First, one surface is carefully worked down 

 on the stone until it is perfectly plane and smooth. Then some 

 hard balsam is melted upon a glass slip and the smooth surface 

 of the specimen pressed down upon it and held there until the 

 balsam becomes cold and hard. By this means it is firmly 

 fastened to the glass, and can be rubbed down upon the stone 

 until a section of sufficient thinness has been obtained. It is 

 then carefully washed off in water, dried in air, and mounted 



