ox GEOLOGIC HISTORY. 273 



an average proportion of two and a half to one succeeded it, 

 — ^it is the brain of the reptile ; then came the brain ave- 

 raging as three to one, — it is that of the bird ; next in suc- 

 cession came the brain that averages as four to one it is 



that of the mammal ; and last of all there appeared a brain 

 that averages as twenty-three to one, — reasoning, calculating 

 man had come upon the scene. All the facts of geological 

 science are hostile to the Lamarckian conclusion, that the 

 lower brains were developed into the higher. As if with 

 the express intention of preventing so gross a mis-reading of 

 the record, we find, in at least two classes of animals, — fishes 

 and reptiles, — the higher races placed at the beginning : the 

 slope of the inclined plane is laid, if one may so speak, in the 

 reverse way, and, instead of rising towards the level of the 

 succeeding class, inclines downwards, with at least the effect, 

 if not the design, of making the break where they meet ex- 

 ceedingly well marked and conspicuous. And yet the record 

 does seem to speak of development and progression ; — not, 

 however, in the province of organized existence, but in that 

 of insensate matter oubject to the purely chemical laws. It 

 is in the style an(/ character of the dwelling-place that gradual 

 improvement seems to have taken place, — not in the func- 

 tions or the rank of any class of its inhabitants ; and it is with 

 special reference to this gradual improvement in our common 

 mansion-house the earth, in its bearing on the " conditions 

 of existence," that not a few of our reasonings regarding the 

 introduction and extinction of species and genera must proceed. 

 That definite period at which man was introduced upon 

 the scene seems to have been specially determined by the 

 conditions of correspondence which the phenomena of his 

 habitation had at length come to assume with the predestined 

 constitution of his mind. The large reasoning brain would 

 have been wholly out of place in the earlier ages. It is in- 

 dubitably the nature of man to base the conclusions which 



