TECHNIQUE 55 



adding it to the day's load. A small quantity may be 

 put into a gauze bag (say, a small butterfly-net) or a 

 fine sieve. If the rubble is dry, a short spell of vibra- 

 tion will drive the finest powder through the mesh, 

 and the gritty residue can be inspected with a hand- 

 lens. If it is wet, the same result may be obtained by 

 vigorously shaking the container under water. It is 

 usually possible to detect small fossils in the residue, 

 and to form an estimate of their relative abundance. 

 But failure to find them by this rough method is no 

 proof of their total absence ; it should merely influence 

 the collector in determining the bulk of material worth 

 carrying. Students of Microzoa are well advised to 

 bring away samples of all sedimentary rocks exposed 

 in each section. Many compact masses may be resolved 

 into powder by suitable means, while the others can 

 be sliced for microscopic examination. Experience 

 will soon show the types of matrix most likely to yield 

 small fossils. 



(IV) FIELD PREPARATION 



The limitations of human strength demand that the 

 items of a day's " bag " shall have the smallest size 

 compatible with their safety. Hence, when a fossil is 

 firmly embedded in matrix, it is expedient to reduce 

 the bulk of the block. But it is never safe to aim at 

 complete extraction of the fossil at this stage. Not 

 only does adherent matrix act as a protection to the 

 specimen during carriage, but it often affords useful 

 proof of the layer from which it was collected. When 

 possible, use of a hammer in the rough trimming of 

 specimens should be avoided. The vibration caused 

 by blows often shatters the fossil, even though care is 

 taken to strike distant parts of the block; while the 

 uncertainty of the direction of fracture involves risks 



