12 INTRODUCTION. 



other regularly, and in their proper order. This is because 

 the particular region where this occurs was always submerged 

 beneath the sea while these formations were being deposited. 

 There are, however, many more localities in which one would 

 find the Carboniferous Rocks resting unconformably upon the 

 Silurians without the intervention of any strata which could be 

 referred to the Old Red Sandstone. This might arise from 

 one of two causes : i. The Silurians might have been elevated 

 above the sea immediately after their deposition, so as to form 

 dry land during the whole of the Old Red period, in which 

 case, of course, no strata of the age of the Old Red Sandstone 

 could possibly be deposited. 2. The Old Red Sandstone might 

 have been deposited upon the Silurian, and then the whole 

 might have been elevated above the sea, and subjected to an 

 amount of denudation sufficient to remove the Old Red Sand- 

 stone entirely. In this case, when the land was again sub- 

 merged, the Carboniferous Rocks, or any younger formation, 

 might be deposited directly upon Silurian strata. From one 

 or other of these causes, then, or from subsequent disturbances 

 and denudations, it happens that we can rarely find many of 

 the primary formations following one another consecutively 

 and in their regular order. 



In no case, however, do we ever find the Old Red Sand- 

 stone resting upon the Carboniferous, or the Silurian Rocks 

 reposing on the Old Red. We have therefore, by a com- 

 parison of many different areas, an established order of succes- 

 sion of the stratified formations, as shown in the subjoined 

 ideal section of the crust of the earth (fig. 2). 



The main subdivisions of the Stratified Rocks are -known by 

 the following names : 



1. Laurentian. 



2. Cambrian (with Huronian?). 



3. Silurian. 



4. Devonian or Old Red Sandstone. 



5. Carboniferous. 



8. Jurassic or Oolitic. 



9. Cretaceous. 



10. Eocene. 



11. Miocene. 



12. Pliocene. 



13. Post-tertiary. 



