3i TOWN GEOLOGY. [i. 



known to the unknown, and show you how to 

 explain the latter by the former. Sir Charles Lyell 

 has, I see, in the new edition of his " Student's 

 Elements of Geology," begun his book with the 

 uppermost, that is, newest, strata, or layers ; and has 

 gone regularly downwards in the course of the book to 

 the lowest or earliest strata; and I shall follow his 

 plan. 



I must ask you meanwhile to remember one law or 

 rule, which seems to me founded on common sense; 

 namely, that the uppermost strata are really almost 

 always the newest; that when two or more layers, 

 whether of rock or earth or indeed two stones in the 

 street, or two sheets on a bed, or two books on a table 

 any two or more lifeless things, in fact, lie one on 

 the other, then the lower one was most probably put 

 there first, and the upper one laid down on the lower. 

 Does that seem to you a truism ? Do I seem almost 

 impertinent in asking you to remember it ? So much 

 the better. I shall be saved unnecessary trouble 

 hereafter. 



But some one may say, and will have a right to 

 say, " Stop the lower thing may have been thrust 

 under the upper one." Quite true : and therefore I 

 said only that the lower one was most probably put 

 there first. And I said " most probably/ 7 because it 

 is most probable that in nature we should find things 

 done by the method which costs least force, just as 

 you do them. I will warrant that when you want to 

 hide a thing, you lay something down on it ten times 

 for once that you thrust it under something else. You 

 may say, ' ' What ? When I want to hide a paper, 

 say, under the sofa-cover, do I not thrust it under ? " 



