THE HISTORY OF ORGANISMS. 7 



periods of living of the several organisms under our investiga- 

 tion ; and second, that there is genetic affinity between the 

 organisms now living and those that have lived in the past. 

 We assume that series of organisms genetically connected 

 have lived during geological time. 



Geological Formations. It will be necessary to particularly 

 consider the nature of geological formations, for in them are 

 found the fossils, and from them is derived the evidence of 

 the history which we are to read. We must consider how the 

 formations were made, how the chronological scale is deter- 

 mined and what reliance may be placed in it. We must con- 

 sider the manner of deposition, and under what condition fos- 

 sils have been preserved ; we must examine into the perfec- 

 tion or imperfection of the record, what has transpired to 

 destroy the record, and hence how we can supplement the 

 record we possess. Hence, geological classifications must be 

 critically examined and analyzed. This will occupy the 

 earlier chapters. 



The Organism. The second step will be to learn what the 

 organism is and what it is not ; what is meant by species 

 and genera ; what is the nature of systematic classification ; the 

 meaning of generation, race, modification, struggle for exist- 

 ence, geographical distribution, and many kindred terms. 



Races and their History. This will bring us to the third 

 part of our subject, the specific study of races, their geologi- 

 cal history, and the laws to be gathered from their study. 

 The history of the organism may be viewed under two lights ; 

 as we consider the development of the individual as it passes 

 from the germ to the fully organized adult, or as we consider 

 one particular kind of organism as assuming the features 

 which now characterize it from some other different kind of 

 organism which preceded it. In the one case that which is 

 continuous in the history is the individual life which develops, 

 in the other case that which is continuous is the race which 

 evolves. 



The Chronological Scale. In any discussion of history the 

 first and essential element of fact to be established is a relia- 

 ble chronological scale by which to mark off the relations of 

 successive events or epochs of the history. In studying the 



