372 THE POPULAR SCIENCE MONTHLY. 



botany, a knowledge of which may appear to the student as having 

 little connection with geology." 



During the later half of the third period, greater progress was 

 made, and before its close geology was thoroughly established as a 

 science. Let us consider for a moment what had really been accom- 

 plished up to this time. 



It had now been proved beyond question that portions at least of 

 the earth's surface had been covered many times by the sea, with alter- 

 nations of fresh water and of land ; that the strata thus deposited 

 were formed in succession, the lowest of the series being the oldest ; 

 that a distinct succession of animals and plants had inhabited the earth 

 during the different geological periods ; and that the order of succes- 

 sion found in one part of the earth was essentially the same in all. 

 More than 30,000 new species of extinct animals and plants had now 

 been described. It had been found, too, that from the oldest forma- 

 tions to the most recent, there had been an advance in the grade of 

 life, both animal and vegetable, the oldest forms being among the sim- 

 plest, and the higher forms successivelj'^ making their appearance. 



It had now become clearly evident, moreover, that the fossils from 

 the older formations were all extinct species, and that only in the most 

 recent deposits were there remains of forms still living. The equally 

 important fact had been established that in several groups of both 

 animals and plants the extinct forms were vastly more numerous than 

 the living, while several orders of fossil animals had no representa- 

 tives in modern times. Human remains had been found mingled with 

 those of extinct animals, but the association was regarded as an acci- 

 dental one by the authorities in science ; and the very recent appear- 

 ance of man on the earth was not seriously questioned. Another im- 

 portant conclusion reached, mainly through the labors of Lyell, was, 

 that the earth had not been subjected in the past to sudden and vio- 

 lent revolutions ; but the great changes wrought had been gradual, dif- 

 fering in no essential respect from those still in progress. Strangely 

 enough, the corollary to this proposition, that life, too, had been con- 

 tinuous on the earth, formed at that date no part of the common stock 

 of knowledge. 



In the physical world the great law of " correlation of forces " 

 had been announced and widely accepted ; but, in the organic world, 

 the dogma of the miraculous creation of each separate species still held 

 sway, almost as completely as when Linnfeus declared, " There are as 

 many different species as there were different forms created in the 

 beginning by the Infinite Being." But the dawn of a new era was 

 already breaking, and the third period of paleontology we may con- 

 sider now at an end. 



Just twenty years ago, science had reached a point when the belief 

 in " special creations " was undermined by well-established facts, slowly 



