MODE OF PRESERVATION— NAMING OF FOSSILS. 5 



lime of the fossil, and in the end completely silicify it. Such silic- 

 ification is commonly indicated by the formation of " Beekite 

 rings," numerous small rings scattered over the surface of the shell 

 or coral, and having at their centers a tubercle of silica. Silicified 

 fossils commonly weather out in relief (though this is true also of 

 calcified fossils), and they may be separated from calcareous rock 

 matrix by acid. Silicification commonly destroys the minute 

 structure of the organism while preserving its form. Many other 

 minerals replace organisms, most common next to silica being 

 iron pyrites. Wood may be partially or wholly silicified. In 

 the first case the silica merely fills the cells and ducts, while in 

 the second case the woody tissue is also replaced. Leaves may 

 leave a picture of themselves in precipitated iron oxide, or they 

 may be replaced by various minerals, or merely remain behind as 

 a film of carbon. 



Distortion often results from silicification, while crystallization 

 frequently accompanies calcification, especially among the echi- 

 noderms. 



Meclianical Deformation. — When rocks haye suffered compres- 

 sion, fossils are commonly distorted. When the pressure is ver- 

 tical the fossils are flattened out. This is frequently the case in 

 undisturbed shales, where the compression of the beds, through 

 pressure of overlying rocks, flattens out the shells, which in inter- 

 calated limestones or sandstones retain their normal form and ro- 

 tundity. Where lateral compression has affected the strata various 

 distortions result, which often may make the determination of the 

 fossil a matter of difficulty. Brachiopod shells may in this way be 

 made to resemble pelecypod shells. 



The Naming of Fossils. 



Each fossil is designated by a binomial term, the first part of 

 which is the generic and the second the specific name. Generic 

 names are written with an initial capital letter, specific names always 

 begin with a small letter, even if derived from proper names. 

 Thus Heliophyllnm Jialli is correct, while Heliophyllum Halli is in- 

 correct. The ending of the specific name (except nouns) must cor- 

 respond to the gender of the generic name. The common endings 

 are us, a, um, or is, is, e, for masculine, feminine and neuter gender, 

 respectively. Specific names derived from proper nouns remain 



