MATERIALS 39 



(C) THE PRESERVATION OF FOSSILS 



(I) COMPLETE OR UNCHANGED PRESERVATION 



The soft tissues of Invertebrates are of such texture 

 that their preservation, even for short periods after 

 death, requires rapid and exceptional processes. Such 

 processes are likely to develop protective matrices 

 which are themselves doomed to decay. Whereas 

 plants may grow in such profusion that their matted 

 remains exude antiseptic fluids sufficient to prolong 

 the existence of cell-contents (thereby giving oppor- 

 tunity for more perpetual preservation), animals rarely 

 congregate, either in life or death, in masses comparable 

 with peat. Even in coral-reefs the polyps are separated 

 by disproportionate quantities of mineral matter incap- 

 able of retarding the chemical dissolution of its builders. 

 Few Invertebrates have tough "skins," although the 

 ligaments of Pelecypoda have merit in this respect. 

 Such ligaments are occasionally preserved (with but 

 slight shrinkage or carbonization), and may be found 

 in rock-systems as far back as the Jurassic (PI. iii. fig. i). 

 They are most often met with in clays or rocks with 

 much argillaceous content, and are perhaps least rare in 

 the Dorsetshire Corallian and London Tertiaries. 



The most perfect type of preservation is found in 

 masses of amber that enclose small insects. The sticky 

 resin that may entangle and enshroud organisms can 

 do so only when freshly extruded, and so is available 

 for aseptic preservation of terrestrial or aerial forms 

 alone. Since amber is bound to undergo gradual 

 carbonization, the beautiful and effective mode of 

 fossilization that it lends to types of Invertebrates 

 otherwise rarely preserved can be but temporary ; such 

 evidence does not extend back beyond the Tertiary stage. 



