XI 



THE COLLECTION AND PRESERVATION OF 

 FOSSILS 



REFERENCE has incidentally been made in previous 

 chapters to some of the conditions of preservation of 

 fossils. They may here be summarized : 



1. Very rarely is an animal or plant body preserved 

 whole : the case of insects in amber a fossil resin which 

 enveloped them as it trickled down the bark, preserved 

 them by its antiseptic character, and became hardened 

 by loss of its volatile constituents is perhaps the only 

 case. The frozen mammoths of Siberia are not true 

 fossils, as they are not entombed in sediments. 



2. While the soft parts decay, the hard parts mainly 

 of mineral substance, but sometimes organic may be 

 preserved without any chemical change. This is a very 

 common case among animals, if we interpret the term 

 "chemical change" rather broadly. Some amount of 

 chemical change is almost inevitable the filling-up of 

 minute cavities with secondary mineral matter, as in 

 echinoderm skeletons and vertebrate bones, is rarely 

 escaped. Among plants, where the hard parts are 

 organic, some carbonization nearly always takes place ; 

 but in the paper-coal of Tula, in Russia, the cuticles of 

 the plants are said to be absolutely unchanged. 



3. The hard parts may he preserved, but with more or 

 less complete chemical change. If the original skeleton 

 was of calcite this may be replaced by silica, dolomite, 



345 



