22 NATURAL HISTORY OF 



the philosophy of early history, will immediately recog- 

 nize, notwithstanding that they come upon him under 

 the combinations of a fresh aspect ; but, where traces 

 occur of great nations, and especially of those that have 

 had, or still continue to have, a marked influence on 

 human destinies, a certain extent of detail, we trust, 

 will be justifiable. 



On questions of antiquity, involving periods of time, 

 and on others, which relate to the measurements of 

 distance between geographical points, it may be well 

 to bear in mind, that the first having no physical in- 

 strumentality, is liable to be contracted to within as- 

 sumed chronological data, commencing at arbitrary 

 epochs, not supported by researches in geology, and 

 often appearing to be of insufficient duration ; while 

 the second being based upon measures of length, either 

 undefined, or varying in different places and times, 

 are, from an innate propensity in the human mind to 

 magnify the unknown, stated to be more than the 

 reality. The purpose before us is, however, suffi- 

 ciently attained, by taking given ages for the one and 

 approximation to true distances for the other. We 

 can, by these means, notice a succession of epochs in 

 the conditions of the earth's surface, each adapted to 

 the existence of vertebrated animals, with it appears 

 an atmospheric state, gradually more suited for mam- 

 malia, of certain orders and families, until it became 

 fit for the reception of man, whose creation may have 

 synchronized with the decay and subsequent disap- 

 pearance of a great proportion of the most powerful 



