[21] COLLECTING AND PREPARING FOSSILS — SCHUCHERT. 



and soaked again and again until all are well reduced, but some un- 

 broken pieces will always remain. Wash away all the mud as described 

 above for clay. Then boil in a dish " over a brisk fire for about half an 

 hour, the boiling being continued with occasional changes of water till 

 little or no mud appears." Gray shales usually boil down completely. 



The black sliales, on the other hand, containing considerable proportion of bitumi- 

 nous cement, will not thoroughly break up even after prolonged boiling. 



The drying and steeping here described may be regarded as processes of rapid arti- 

 ficial v^eathering. The effects of the heat of a fire upon shale resemble those of the 

 sun's ri*ys, and the soaking in water is a counterpart of the action of rain. It is 

 surprising how easily hard, compact shale, which can witli difficulty be broken or 

 split with a hammer, may, by the method above specified, be reduced to dust or to 

 fine granular debris, from which even delicate shells may easily be picked out entire. ^ 



Washing for microscopic organisms. — One of the first essentials is that all glass- 

 ware, pipettes, etc., designed for this use be absolutely clean, and that only river 

 or rain water, recently filtered, be used; otherwise you will probably find on 

 your slides many beautiful organisms that do not belong to the substance under 

 examination. 



Clay. — In preparing most of the samples of clay/ we would put about 1 ounce 

 of the material, and the same amount of common washing soda, into a druggist's 

 two-quart clear-glass packing bottle, not over one-fourth filled with water, and let it 

 remain twelve to twenty-four hours, frequently shaking the bottle, so as to thor- 

 oughly break up the clay. Now fill the bottle with water, and after twenty-five 

 minutes carefully pour off" the upper three-fourths of it. Again fill with water, and 

 in twenty-five minutes decant as before; repeating this at twenty-five minute inter- 

 vals until the upper three-fourths of the water iu the bottle, after a twenty-five 

 minute rest, will be nearly clear. A large amount of the fine sand, clay and the 

 soda, has by this process been washed away, and the action of the soda has broken 

 up the clay and removed most of the adhering material from the fossils. Now mount 

 a few microscope slides from the residuary sand, etc., at the bottom of the bottle, 

 by taking up with a pipette (a piece of small glass tubing makes the best pipette) 

 a small amount of the material; scatter very thinly over tlie middle of the slides; 

 dry them thoroughly over an alcohol lamp, or in some better way, and while hot, cover 

 the dry material with a few drops ©f Canada balsam, keeping the slides quite warm 

 until the balsam will be hard when cold. As these " trial slides " are seldom of any 

 value, it is not necessary to use cover glasses if the balsam is hardened, as above 

 directed. A careful examination of these slides under the microscope with a good 

 quarter or half inch objective will decide as to the value of the material under 

 observation, and if it proves to be only sand, pour it all out, wash the bottle, and 

 again try the same process with another sample of clay. But if the slides show a 

 few good fossils, the next step is to separate them as much as possible from the mass 

 of sand, etc., with which they are associated. In this, as in the first washing, 

 specific gravity will do most of the work. Pour off most of the water and put the 

 shells, sand, etc., into a 4-ounce beaker (or glass tumbler), wash oat the bottle, fill 

 the beaker about three-fourths full of water, and after it has rested ten minutes, 

 pour three-fourths off the top through a glass funnel into the bottle, repeating this 

 five or six times. As in the first washing, mount and examine a few slides from the 

 material at the bottom of the bottle, mounting and preserving slides, if found to be 

 of value. If nothing of value is found pour out the contents of the bottle, and fill 

 up again as before from the beaker, after five minutes rest repeating these washings 

 and examinations at shorter resting intervals, of, say, three, two, and one minute, 

 or less, until nothing but the coarsest sand remains in the beaker. In that there 



' Sir Archibald Geikie, Text-Book of Geology, pp. 671, 672, 1893. 



