RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 335 



VKKTKI5KA I A. 



Although the Vertebrata constitute the highest division of the animal 

 kingdom, for the reasons just mentioned, comparatively few of them 

 except the fishes have a direct bearing upon any inquiry concerning 

 the character of formerly existing bodies of water. That is, much the 

 greater part of all the other vertebrates consist of land animals the 

 natural habitats of which have at best only an indirect relation to the 

 character of the waters in the sediments of which their remains may 

 find intombment. 



Mammalia. — The Mammalia are so generally dwellers upon the dry 

 land that while a few are amphibious in their habits only the orders 

 Cetacea and Sirenia and the Phocidae and Odobaenidae of the order Car- 

 nivora are confined to an aquatic habitat, at least so far as concerns 

 their locomotion. Besides this, all these animals being air-breathers 

 their aquatic habitat may be regarded as a matter of special adapta- 

 tion. 



Fossil remains of any of the larger Cetacea may be taken as presump- 

 tive evidence of the marine origin of the deposits in which they maybe 

 found, but so many of the smaller members of that order live in estua- 

 ries that other evidence is usually required to determine the character 

 of the deposits in which fossil remains of such animals occur. Because 

 the structure and habits of the Sirenia restrict them to an estuarineor 

 littoral habitat, fossil remains of such animals have much significance 

 as to the character of the deposits in which they may occur, and as to 

 the proximity of the land to the place where such deposits were made. 

 Although the Phocidae and Odobaenidae usually inhabit marine waters, 

 they often range into estuaries and occasionally, but rarely, some of the 

 former inhabit fresh waters. Therefore, fossil remains of such animals 

 is strong presumptive, but not positive, evidence of the marine origin 

 of the formations in which they may be found. 



The foregoing remarks apply to those mammals which live in, or 

 habitually resort to the water, but the larger part of all discovered fos- 

 sil mammalian remains are those of strictly land animals. The manner 

 in which such remains have found intombment in aqueous sediments, 

 and the probable reasons why they are much oftener found in nonma- 

 rine than in marine formations have been indicated on preceding pages. 



A res. — As a class, birds have little bearing upon the subject of this 

 review, because their respiration is aerial, and comparatively few of 

 them habitually live in the water as a permanent habitat. Further- 

 more, with apparently the exception of the Spheniscidae and some of 

 the Laridae, those which resort to an aquatic habitat find saline and 

 fresh waters equally congenial. Avian fossil remains are therefore of 

 comparatively little value as indicating the character of the water in 

 which any given formation was deposited. Still, as is the case with 

 the mammals and other land animals, avian remains are more likely to 

 be found in the sediments of inland than of marine waters. 



