BULLETIN 39, UNITED STATES NATIONAL MUSEUM. [20] 



of the soft condition of many sediments, such as friable sandstones, 

 soft shales, chalks, and marls. In general, fossil plants can not be 

 washed, since these are usually preserved in soft materials. Verte- 

 brates, also, do not heed this preliminary treatment, as most specimens 

 will first require the work of a "stone mason" or a i^reparator. 



Clay and marl icashing. — Paleozoic fossiliferous clays which are to be 

 washed for small and young fossils should be first dried in an oven or in 

 the sun and then well soaked in water for a day or more before washing. 

 A deep pan or bucket serves well for this purpose, using the hands 

 to stir the mass around, but do not get too much mud in suspension, 

 since in pouring off the muddy water many of the smaller organisms 

 are liable to be carried away. The writer has tried nests of sieves of 

 various size meshes, placing the soaked mud in the upper coarse one, 

 and using a stream of running water as the cleanser. But to catch all 

 the smaller fossils, which is the main object, the lower sieve must be 

 very fine (a bolting cloth), and this is soon clogged with mud, prevent- 

 ing further washing. The contents of the lower sieve must be washed 

 alone, and in the end a pan is more productive for rapid work, with 

 equally good results. After the washed earth has been dried it should 

 be sifted, to facilitate picking, into three grades, using sieves of 6, 18, 

 and 38 meshes to the inch. The coarser material can be assorted with 

 the unaided eye, but the finer grades will have to be selected under a 

 low-power lens. A moistened camel's-hair brush is the best tool with 

 which to pick up these smaller organisms. If the brush is held in the 

 end of a small vial a twirl of the fingers will readily remove the attached 

 fossil. 



The material derived from washing slabs and the residuum from etch- 

 ing by the muriatic- acid process should be washed in the same way as 

 described above for clay. Great care, however, must be taken in wash- 

 ing etched fossils, since quite often these consist of but a thin outer and 

 inner layer, the intermediate space being hollow and therefore very 

 delicate. The surface detail of such fossils is preserved better than on 

 fossils weathered out in nature. 



Washing Paleozoic fossiliferous clay for mature or large fossils is 

 sometimes resorted to on a large scale. In England, Mr. Maw prepared 

 for Thomas Davidson several tons of Dudley clay (Upper Silurian) in 

 tubs beside a stream. His results were remarkable. 



Marls frequently yield good fossils when carefully washed. It is 

 often the case, however, that marl fossils are quite soft or chalky. 

 Such, of course, can not be washed, and must be picked out and 

 cleaned dry. If hard, the marl is laid in a coarse sieve, and washed in 

 a stream of running water until clean. Some of the fine material thus 

 carried away should be caught and washed separately for foraminifera 

 or other microscopic organisms by the method described beyond. 



Washing univeathered shale. — Dry the shale well in an oven, and then 

 soak it in water till it crumbles. The larger fragments can be dried 



