GENERAL PRINCIPLES. 257 



divisions of time are recorded in separate rock systems, 

 rock series, wok formations, according to their importance. 



2. These divisions of time, in human history, usually 

 graduate, more or less insensibly, into each other. Yet, 

 at certain points, called revolutions, the steps of change 

 are more rapid. 80, also, in geological history, the eras, 

 ages, periods, etc., usually graduate into each other. 

 And yet there are certainly here, also, times of revolution, 

 in which the steps of change are far more rapid. Thus all 

 history, human or geological, consists of periods of com- 

 parative quiet and prosperity, during which the forces of 

 change are gathering strength ; and periods of revolution, 

 when these forces show themselves in conspicuous effects. 



3. In human history, what is distinctively called an age, 

 is marked by the dominance of some characteristic social 

 force or principle. Thus, we have had an age of chivalry, 

 and we look forward to an age of reason. So, also, in 

 geology, what is distinctively called an age, is marked by 

 the dominance of some particular class of animals or 

 plants. Thus, we have an age of mollusks, an age of 

 fishes, an age of reptiles, etc., in which these several 

 classes are successively the dominant types. Now, since 

 the divisions graduate into each other, it is to be expected 

 that the characteristic of each age will commence in the 

 preceding age. This we shall call the law of anticipation. 



4. In human history each dominant characteristic, of 

 course, arises, culminates, and declines ; but it does not, 

 therefore, perish. It only becomes subordinated to the 

 next coming and higher characteristic, and society thus 

 becomes not only higher and higher, but also more and 

 more complex in its structure. So, also, in geology we 

 shall find that as each dominant class culminates and 

 declines, it does not perish, but only becomes subordi- 

 nated to the incoming and higher dominant class, and 

 thus the whole organic kingdom becomes not only higher 

 and higher, but also more and more complex in its struc- 



LE CONTE, GEOL. 17 



