178 MEANING OF THE SYSTEM. 



Examples of Mammalia, although scarce, are found in the upper 

 Triassic beds, and also in the Jurassic. Such Mammalia belong 

 without exception to the lowest grade of Marsupials. Flowering 

 plants appear for the first time in the chalk, as do the oldest remains 

 of distinctly bony fishes. 



Flowering plants and Mammalia and amongst the latter the 

 highest order of Apes is represented so preponderated in the 

 tertiary period that it has been called the period of leafy forests and 

 Mammalia. The plants and animals of the upper tertiary beds show 

 a gradually increasing resemblance to those of the present time, the 

 higher we ascend in the series. Numerous lower animals and plants 

 are identical, not only generically but also specifically with those 

 now living, and the genera and species of the higher animals have 

 a greater resemblance to those of the present time. With the 

 transition to the diluvial and recent epoch, the number and area of 

 distribution of the higher types of flowering plants increase, and in 

 every order of Mammalia we find f orms whose structure is specialized 

 more and more in definite directions, and which therefore appear 

 more perfect. In the diluvial age we find the first unmistakable 

 traces of the existence of Man. His history and the development of 

 his civilization has occupied only the last portion of the recent period 

 which has been relatively so short. 



Despite its great incompleteness the geological record affords 

 sufficient material to prove the existence of a progressive develop- 

 ment from simple and lower grades of organization to higher, and 

 to confirm the law of a progress towards perfection in the succession 

 of the groups. We are indeed unable to make use of more than 

 a small period of the time that has been occupied in this progress 

 towards perfection of organisms, since the organic world of the most 

 ancient and extensive periods has completely disappeared from the 

 record. 



If, after the above discussion, we consider the hypothesis of Trans- 

 mutation of Species and of Descent to have a firm foundation on fact, 

 we must concede a high value to Darwin's theory of Selection as an 

 explanation of the manner in which the transmutation of species has 

 been effected. 



There are yet natural historians who admit the great changes 

 which the animal and vegetable world have undergone, and yet 

 combat the Darwinian principle of Selection, without being able to 

 give any other explanation. The phenomena of gradual progress 

 towards perfection agree very well with the theory of Selection. 



