CHAPTEE VII. 



GENERAL CONCLUSIONS. 



These have, perhaps, been sufficiently indicated in an 

 incidental manner in the preceding pages ; but it may be 

 well here to note some results of a less special character 

 and bearing on larger biological and cosmical questions. 



With reference to the life of the Pleistocene period, one 

 can scarcely fail to observe that, whatever may have been 

 the lapse of geological time from the period of the oldest 

 boulder-clay to that in which we live, and great though 

 the climatal and geographical changes have been, we 

 cannot affirm that any change, even of varietal value, has 

 taken place in any of the species of the above lists. 

 This appears to me a fact of extreme significance with 

 reference to theories of the modification of species in 

 geological time. No geologist doubts tliat the Pleistocene 

 was a period of considerable duration. The great eleva- 

 tions and depressions of the land, the extensive erosions, 

 the wide and thick beds of sediment, all testify to the 

 lapse of tune. The changes which occurred were fruitful 

 in modifications of depth and temperature. Deep waters 

 were shallowed, and the sea overflowed areas of laud 

 The temperature of the waters changed greatly, so that 

 the geographical distribution of marine animals was 



