113 



11. Mijukiing MaterinJ. (Jiitta-perchn, ^Ai^ch comes in 

 thill sheets and can be obtained at any rubber store, is 

 nsefnl for takini;- impressions from the moidds of fossils. 

 '"Modeling composition No. l2, medium" — a dentist's wax 

 of a red color, and obtainable in half-])ound boxes at any 

 dentists' supply store — will free piently be found more useful 

 than o-utta-percha . 



o. Chemicals. Hydrochloric acid, caustic potash (sticks), 

 arid vinegar- are necessary for* cleaning and etching. 



Laboratory Work. As soon as the specimens are un- 

 packed, place them in the paper trays, making sure that 

 each traj \H provided with a co})y of the proper field label. 

 The si)eciinens may be roughly assorted, but they must 

 never be left without labels. The clay is washed off by use 

 of the coarse brushes, and the superfluous rock is removed 

 with the cutting forceps, or other tools. If the specimen is 

 broken, clean the parts and then glue them together, placing 

 them on a l)ed of sand until dry. The sand will support the 

 unequal ])arts, and prevent them from separating, as they 

 would if unsupported. In cleaning specimens with chisel 

 and mallet alwa^'s place them on a sand bag. 



To remove hard clay or shale from delicate specimens, 

 where cutting is impossible, ])lace small tablets of caustic 

 potash, cut from the sticks, upon the shale matrix, and 

 leave it for some hours. The calcareous shale will be disin- 

 tegrated and can be washed off. Repeat this until the s])eci- 

 men is clean. After that, wash the specimen thoroughly for 

 some days in several changes of water, to which a, few droi)S 

 of hydrochloric acid have been added, to remove all the 

 potash, otherwise the specimen may, in the course of time, 

 disintegrate. Specimens from the Encrinal and the other 

 limestone beds may be cleaned with acid, the final etching- 

 being done with dilute vinegar. 



Ohtainuig Fossils from the Disintegrated Shales. Tlie 

 shales have freiiuently disintegrated into clay. To obtain 

 the small fossils from these the following method of 



