CHAPTER III. 



THE RELATION OF MAKIXE BIO.\0:iIV TO STRATIGHAPHY. 



Marine Bionomy is tliat division of thalassogTa|)liy (ji- 

 oceanog,TaphY which deals witli tlie nature and distribution 

 of marine organisms, and their relation to the environment. 

 It is a strictly geological study, for thalassography itself is 

 a branch of physiography, which in tnrn is that branch of 

 geology which deals with the present surface features of the 

 earth, and the causes which have produced them. Marine 

 bionomy is, in fact, the study of the pahpontology of the 

 present geologic epoch in its marine aspect, carried on under 

 the most favorable circumstances, by contemporary observ- 

 ers. 



In studying the laws of the distribution of animal and 

 plant life in the sea, we must consider two distinct phases of 

 our subject: first, the physical conditions of the sea. and, 

 secondly, the nature and habits of the organisms, i.e., their 

 bionomic characteristics. If the two are harmonious in a 

 given case, it is evident that the locality considered can be 

 inhabited by the organism in question. Under physical 

 conditions we must include the presence of suitable food in 

 sufficient quantity, and the absence or paucity of competing 

 organisms. 



We may consider the physical conditions of the sea in 

 three aspects: climatic, topographic, and organic. The cli- 

 mate of the sea is much moi-e uniform than that of the land. 

 It is true, that in the very shallow parts of the sea the 

 water is often heated to such a degree as to make these 

 regions uninhabitable for most aninu\ls. Ordinarily, how- 

 ever, the continual change of water, due to tidal and other 

 currents, is sufficient to keep the temperature at a modei'- 

 ately low, and more or less uniform, degree. The daily 

 range of temperature in the sea is of less importance to 



