The Principles of Palaeontology. 133 



variations of physical conditions ; from the groupings of forms 

 which are found in certain layers, a conclusion can be drawn 

 regarding the conditions in which the deposits were made ; the 

 fauna of a deep sea is distinguis liable from that of shallow 

 water, shore, estuary, or coral reefs. We can gain some infor- 

 mation regarding climatic conditions and can even, for some 

 epochs, form charts to indicate equal atmospheric temperature. 

 It is then easily seen what services Palaeontology has already 

 rendered and still continues to render to Geology, and if this last- 

 named science now possesses other methods of investigation, if 

 it engages in the study of phenomena of a purely physical order, 

 such as the displacements and formation of rocks, it nevertheless 

 constantly profits by the incessant progress which has been made 

 by .the study of fossils. 



Inversely, Palaeontology can not exist without Stratigraphy, 

 and looks for support to the data of this science. In studying 

 the relationships between organisms, it is requisite to ascertain 

 with the greatest possible precision the epochs at which they 

 have lived. This is no reasoning in a circle, for the relative 

 age of layers is determined primarily, by their order of strati- 

 graphical superposition. The geologist discerns in the order in 

 which they present themselves on the same vertical line, the age 

 of the deposits with the faunas they contain. 



Palaeontology serves then, so to say, as a bond of union between 

 Biology and Geology, between the study of living beings and 

 that of inanimate nature. Its limits in regard to these two 

 sciences are very difficult to fix. But if the object of palaeon- 

 tologic researches seems to make this science appear rather as a 

 branch of Biology, various circumstances have led, most natural- 

 ists to hold a contrary opinion. Geologists have a good right to 

 claim most of the discoveries which were made in Palaeontology 

 until within the last few years. 



This fact explains itself ; it has been for the purpose of exam- 

 ining the geologic deposits and ascertaining the stratigraphic 

 characters of a region, that naturalists have undertaken the 

 often long and painstaking researches which have resulted in the 

 discovery of fossils. There are geologists who, after having 

 secured from the rocks, often with great labor, the fossils 

 discovered therein, have furthermore carefully prepared them 



