212 Report of the State Geologist. 



the other hand, the carhonate of lime in the calcareous parts 

 of these skeletons, being dissolved by water containing car- 

 bonic acid, bones and shells finally disappear, whether in 

 fresh or salt water. Thus, at present, it may happen that the 

 great depths may be found destitute of the shells of Mol- 

 lasks and Foraminifera, which are abundant at the surface, 

 the remains having been dissolved before they reached the bottom 

 of the sea, though found in great abundance in deposits made at 

 a lesser depth. 



It follows, then, that the remains found where they have been 

 deposited from the water, were covered by sediments in a rela- 

 tively short time, and even thus they are not entirely guarded 

 against destruction. When the fossil if erous deposits are elevated 

 above the water, they are exposed anew to the action of rains, 

 whose dissolving properties are extremely active, and calcareous 

 matter runs another chance of disappearing. We have indicated 

 i a fine, that as to animals of the Precambrian epoch the thermic 

 and chemic phenomena have so altered the nature of the rocks 

 that every trace of living creatures has disappeared. 



These conditions being understood we will proceed to a rapid 

 exposition of the processes which permitted the fossilization of 

 animals and plants. 



Fossilization of animals. — Under the most favorable con- 

 ditions, the entire organism, including the soft parts, has left 

 impressions which allow the re-establishing of the form, and even 

 the investigation of some poiats of its organization. The 

 favored localities where these conditions have been realized 

 are celebrated. The best known case is that of the lithographic 

 schists of the Upper Jurassic in Bavaria. At Kellheim, Eich- 

 stadt and especially at Solenhofen, there have been found, along 

 with multitudes of the fossilized hard parts of animals, impres- 

 sions of Medusae of various species, and of naked Cephalopoda, 

 whose ink-bag with its canal is perfectly recognizable, the sepia 

 being transformed into a mass of fine coal-like granulations. 

 The rock consists of a laminated lithographic limestone of very 

 fine texture, which must have been deposited in the form of soft 

 mud in tranquil waters. The lithographic limestone of Cerin, 

 in Ain, has furnished splendid specimens of the same kind. In 

 England the soft parts of Eelemnitidse have also left some im- 

 pressions. 



Ordinarily traces of the hard parts only are found imbedded 

 in the rock. Such substances are divided into two groups. 



