4 PRINCIPLES OF PALAEONTOLOGY. 



nizable groups of animals and plants were succeeded, without 

 the intermediation of any obvious lapse of time, by other assem- 

 blages of organic beings of a different character. Everywhere 

 they found evidence that the earth's crust had undergone changes 

 of such magnitude as to render it seemingly irrational to sup- 

 pose that they could have been produced by any process now in 

 existence. If we add to the above the prevalent belief of the 

 time as to the comparative brevity of the period which had 

 elapsed since the birth of the globe, we can readily understand 

 the general acceptance of some form of catastrophism amongst 

 the earlier geologists. 



As regards its general sense and substance, the doctrine of 

 catastrophism held that the history of the earth, since first it 

 emerged from the primitive chaos, had been one of periods of 

 repose, alternating with catastrophes and cataclysms of a more 

 or less violent character. The periods of tranquillity were sup- 

 posed to have been long and protracted ; and during each of 

 them it was thought that one of the great geological " forma- 

 tions " was deposited. In each of these periods, therefore, the 

 condition of the earth was supposed to be much the same as it 

 is now sediment was quietly accumulated at the bottom of the 

 sea, and animals and plants flourished uninterruptedly and in 

 successive generations. Each period of tranquillity, however, was 

 believed to have been, sooner or later, put an end to by a sud- 

 den and awful convulsion of nature, ushering in a brief and 

 paroxysmal period, in which the great physical forces were 

 unchained and permitted to spring into a portentous activity. 

 The forces of subterranean fire, with their concomitant phe- 

 nomena of earthquake and volcano, were chiefly relied upon as 

 the efficient cause of these periods of spasm and revolution. 

 Enormous elevations of portions of the earth's crust were thus 

 believed to be produced, accompanied by corresponding and 

 equally gigantic depressions of other portions. In this way new 

 ranges of mountains were produced, and previously existing 

 ranges levelled with the ground, seas were converted into dry 

 land, and continents buried beneath the ocean catastrophe fol- 

 lowing catastrophe, till the earth was rendered uninhabitable, 

 and its races of animals and plants were extinguished, never to 

 reappear in the same form. Finally, it was believed that this 

 feverish activity ultimately died out, and that the ancient peace: 

 once more came to reign upon the earth. As the abnormal 

 throes and convulsions began to be relieved, the dry land and 

 sea once more resumed their relations of stability, the condi- 



