THE HISTORY OF ORGANISMS. 3 



eral course of liberal education. Such a treatment of organ- 

 isms as may be sufficient for the illustration of their history 

 does not necessarily enter into an analysis of the structural 

 characters of any particular species. Hence, from the point 

 of view of a technical course of study in biology, this treatise 

 will seem quite superficial. 



The Geological Aspect of the History of Organisms. — On the 

 other hand, there arc characters distinguishing groups of or- 

 ganisms, evidence of which may be preserved in the rocks, 

 which are of far greater importance than the specific details in 

 indicating the relationship organisms bear to each other, to 

 the conditions in which they have lived, and to the place they 

 have occupied in the history of the life of the globe. Such 

 characters are those which will concern us here. In defining 

 our topic as geological biology, we are not proposing to inves- 

 tigate the anatomical organs and tissues of which particular 

 animals are made, but to review the facts and theories which 

 have led to the belief that each living animal and plant is but 

 the last of a long line of organisms whose remains can be rec- 

 ognized in more or less perfect fossils, and whose varying 

 characters can be traced back into the immense antiquity of 

 geological time. 



Geological History not a Repetition of Like Events, but a Pro- 

 gressive Change of Phenomena. — If there were only repetition of 

 the same things, this would not constitute history. If differ- 

 ent things have succeeded each other, to ascertain the relation- 

 ship borne by those that follow to those that preceded them 

 becomes an important problem. We do not, at the outset, 

 assume to explain the causes, but geology makes the fact 

 clear that there has been a very elaborate history of the or- 

 ganisms that have lived on the earth. The question we pro- 

 pose to answer is, "What are the prominent laws expressed 

 in this history?" 



The geologist observes that there has been a history for 

 the earth itself : the rocks, as geological formations ; the lands, 

 as parts of the crust above the surface of the ocean ; the sur- 

 face of the earth, as a whole, in all its complexity — all these 

 have come to be what they are through innumerable changes. 

 The geological conditions in the past have been associated 



