THE REVOLUTIONS OF THE CRUST OF THE EARTH. 313 



It ha.-> also prepared the way for organized beings; resembling life in 

 its movement, it has rendered life possible, and without it life would 

 cease. It was at first violent and irregular in action, but it prepared 

 inorganic material for organization and actualization, and when the 

 wild elements of nature were exhausted, at the mysterious mandate of 

 creation, we see arise from the bosom of the ocean the first of those liv- 

 ing beings which have taken possession of the earth and of the air. 



The appearance and the development of life is a very important epi >ch 

 in the history of the earth, and as such, as well as on account of the 

 modifications of the crust occasioned by the existence of organisms, we 

 will proceed to consider some important aspects of this phenomenon. 



CHAPTER IV. 



ORGANISMS. 



It is an unusual circumstance, in penetrating the soil even to a slight 

 depth, not to find organic remains. In examining these carefully and 

 comparing them with living organisms differences are found so great 

 that often they cannot be classed with any recent species or even 

 genus. Sometimes there are entire families of which no analogues are 

 found in the living creation, but which nevertheless, judging from the 

 profusion of their fossil remains, must for a considerable time have 

 dominated on account of their numbers and their form in the fauna or 

 the flora of the period in which they existed. " What is the reason of 

 these successive appearances and disappearances ! What laws control 

 these perpetual changes ? What are the causes which destroy a portion 

 of these organisms and preserve others ? These are the most difficult 

 questions biology has to answer ; let us see whether she can satisfy our 

 legitimate curiosity. 



Most of the sedimentary rocks are characterized by the presence of 

 fossil remains, which are peculiar to them. We may say in the present 

 state of science that the chain of organisms is continuous, commencing 

 with the Laurentian formation. We find in the latter remains of mi- 

 croscopic animals, whose presence may be detected by chemical reagents. 



The Silurian formation hitherto has relatively been the richest in 

 organisms. We find in it mollusks and fish. If some of the genera of 

 this formation have for a long time been extinct, others, especially 

 among the mollusks, still exist ; such are the genera Nautilus, Turbo, 

 Buccinum, Turritella, Terebratula, &c. It is in this formation that for the 

 first time we find the remains of plants; these are the fucoitls which, 

 as far as we know, are the first representatives of the vegetable king- 

 dom.* These plants are perpetuated through all the periods, but always 

 under richer and more varied forms. It is important to observe that 

 * Unger, Chluris protoyaa, p. ■-. 



