60 INVERTEBRATE PALAEONTOLOGY 



accounts of many processes are published in " guides " 

 of the British Museum and Smithsonian Institution, and 

 in a paper by Dr. F. A. Bather in vol. viii. of the 

 Museums Journal (1908). In a general introduction to 

 the technique of fossil-preparation, it is more appropriate 

 to convey a series of hints than to describe elaborate 

 schemes rarely adequate for the full solution of particular 

 problems. 



The removal of matrix, and the methods employed 

 therefor, will depend chiefly on two conditions. Matrices 

 differ in texture from soft clay to concretionary matter 

 with the hardness of steel ; while variation in the 

 durability of fossils is hardly less wide. In the relation 

 between these two qualities lies the problem before the 

 worker, whose aim is to destroy the one, and preserve, 

 or even reinforce, the other. Fossils are usually either 

 harder or softer than their containing matrix. Those in 

 soft rocks are usually friable, but the converse is not 

 always true. 



If the fossil is harder than the matrix (whether by 

 original character or petrifaction), and is tolerably 

 coherent, a brush is the safest kind of tool. For calcite 

 shells in loose limestone or clay, no more elaborate 

 apparatus than an old tooth-brush is required. These 

 may be procured in varying degrees of stiffness, or can 

 be graded by cutting the bristles. Rotary brushes may 

 be used in a dental engine, but hand-work is less likely 

 to carry the process too far. In matrices of the nature 

 of chalk, brushing is best carried out in the dry ; though 

 care should be taken to avoid inhaling the dust, which 

 may cause a. kind of "hay-fever." In clays, if the 

 fossils are coherent, the brush may be moistened, but 

 the specimen should never be saturated. It can be 

 occasionally cleared of mud by rinsing for a few seconds 

 under a gentle stream. Fossils too small to be handled 



