^6 T 6 Summary. 



modern times, as dependent on its geology. I have 

 described the classification of all the formations in serial 

 order, and showed the distribution of these rocks over 

 our country, and in doing this I have tried to give a 

 sketch of the physical geography of our area, during 

 the deposition of each successive group of formations. 

 At various times they have all been affected by dis- 

 turbances and denudations, and the grand result is, that 

 where most disturbed, hardened, and denuded, there we 

 have mountainous districts ; for the greater prominence 

 and ruggedness of surface of these regions, arises partly 

 from the hardness of the igneous, metamorphic, and 

 common stratified rocks, partly from the denudations 

 which they have undergone. The Secondary and 

 Tertiary rocks being younger and not so much dis- 

 turbed, have in our country not been so much denuded, 

 and therefore generally form plains and tablelands. 



Moreover, we saw that over all these surfaces, in ad- 

 dition to the vast amount of erosion which must have 

 been effected in Palaeozoic, Secondary, and older Tertiary 

 times, renewed denudations, accompanied by great cold, 

 occurred at a very late epoch. The result of this 

 abrasion has been to cover the surface more or less with 

 loose superficial detritus, upon which part of the fertility 

 of portions of the country and the peculiarity of some 

 of its soils depend. 



I then passed on to notice what I considered to be 

 a very remarkable result of this last great denudation, 

 brought about under the influence of ice, by which the 

 chief part I by no means say all but by which the 

 chief part of the lakes of our country have been formed ; 

 and not of our country alone, but of a large part of 

 the northern, and I have no doubt also of the southern 

 hemisphere. It is a remarkable thing, indeed, to con- 



