136 SUGGESTIONS AS TO COLLECTING 



such as Foraminifera or Sponge-spicnles scattered through it ; and 

 they may be obtained by levigating the loose powder, or, where the 

 material is silicified, by treating it with dilute acid. 



5. Ploughed fields, or fields in the autumn when the crops have 

 been gathered, frequently yield fossils in those instances in which 

 limestone oi' other rocks are near the surface. Molluscan and other 

 shells and many other calcareous fossils often become silicified, and 

 are thus rendered more durable than the limestone matrix ; and 

 they remain when the rest of the rock has been dissolved. Thus it 

 happens that nodules and stones picked from the surface of fields 

 for the repair of roads, etc., often contain good fossils; and heaps of 

 such materials by the roadsides will repay careful scrutiny. 



Treatment of Fossils in the Field. 



1. As a general rule, it is best to do the least possible trimming 

 and cleaning of a fossil in the field. Final preparation for the 

 cabinet can be far better done at leisure afterwards. 



2. Large friable specimens, such as vertebrate skeletons, large 

 Ammonites, or groups of shells, in a matrix which is only moderately 

 hard or liable to fall to pieces on drying, need special treatment. 

 The fossil ought to be first carefully uncovered as it lies in the rock. 

 Then thin paper may be gently pressed over, covering the whole, and 

 as far as possible filling every crevice. Next, plaster of Paris must 

 be poured over this prepared face, and allowed to harden in a moder- 

 ately thick layer. Finally, the specimen may be excavated and 

 transported as a slab, the plaster covering serving as an adequate 

 support. N.B. — Jf paper be not used, the plaster cannot be readily 

 removed from the fossil, and may completely damage it. 



Strips of wood, or thin iron rods, fixed down to the specimen by 

 plaster of Paris and string, may be used, to give rigidity to friable 

 or heavy specimens in lifting them from the quarry to a waggon for 

 transport. 



3. Some large specimens — e.g. bones in Pleistocene deposits — need 

 to be hardened before removal from the matrix. This can be done 

 by uncovering the upper face of the fossil, and pouring slowly upon 

 it a warm, weak solution of gelatine or glue, or the preparation 



