552 PALEONTOLOGY 



Relations to Geology 



It is quite natural that paleontology should still be regarded as 

 a subsidiary part of geology, for it developed from the study of the 

 so-called "figured stones" and "mineral conchology," which were 

 so much discussed more than a century ago. It is based entirely 

 upon fossils, which lose much of their real value unless they are 

 carefully collected by a geologist; and the fossils themselves can only 

 be properly understood by one whose eye is accustomed to the 

 examination of rocks and mineral structures. Moreover, it has been 

 quite clear since the days of William Smith, Cuvier, and Brongniart 

 that fossils always occur in a definite order in the rocks of different 

 ages, so that they afford a means of correlating the formations of 

 widely separated localities whose mutual relationships are otherwise 

 uncertain. To use MantelPs well-known phrase, they are therefore 

 "medals of creation," and an intimate knowledge of them is abso- 

 lutely essential to a geologist when he attempts to determine the 

 relative age of sedimentary deposits which he cannot directly 

 observe in superposition. 



The researches of paleontologists during the last two decades, 

 however, have considerably amplified the original conception of 

 fossils as an index to geological time. So long as detailed observa- 

 tions were mainly confined to one small portion of the earth's sur- 

 face, it was possible to enumerate a few characteristic genera for 

 each stratum of rock; and when geological discoveries began to be 

 made in distant countries, it was found that the general succession 

 of fossil groups of animals was always the same that graptolites 

 and trilobites, for example, were invariably older than ammonites, 

 and that these again always preceded the volutes. At the present 

 day a skilled paleontologist can determine the age of a fauna with 

 much greater precision. The broad outlines of the evolution of most 

 groups of animals have now been ascertained; and when a new set 

 of fossils is discovered in a hitherto unknown formation, the paleon- 

 tologist does not occupy himself so much with the search for familiar 

 genera as with an inquiry into the stage of evolution of the various 

 groups represented. 



This has been pointed out by many authors, but none have stated 

 the case more clearly than Gaudry, who has devoted special attention 

 to the mammalia. 1 The warm-blooded quadrupeds or mammals 

 began as little small-brained animals, each with a continuous series 

 of bluntly-cusped teeth round the edge of the mouth, with flat- 

 tened vertebrae, and with five toes on each foot. A group of fossil 

 remains representing only such animals would be referred to the 

 Eocene Tertiary; and if some of the species had grown to bulky 

 1 A. Gaudry, Essai de PaUontologie Philosophique (1896), pp. 178-197. 



