I.] THE SOIL OF THE FIELD. 35 



No, you lift up the cover, and slip the paper in, and let 

 the cover fall on it again. And so, even in that case, 

 the paper has got into its place first. 



Now why is this ? Simply because in laying one 

 thing on another you only move weight. In thrusting 

 one thing under another, you have not only to move 

 weight, but to overcome friction. That is why you 

 do it, though you are hardly aware of it: simply 

 because so you employ less force, and take less trouble. 



And so do clays and sands and stones. They are 

 laid down on each other, and not thrust under each 

 other, because thus less force is expended in getting 

 them into place. 



There are exceptions. There are cases in which 

 nature does try to thrust one rock under another. But 

 to do that she requires a force so enormous, compared 

 with what is employed in laying one rock on another, 

 that (so to speak) she continually fails ; and instead of 

 producing a volcanic eruption, produces only an earth- 

 quake. Of that I may speak hereafter, and may tell 

 you, in good time, how to distinguish rocks which have 

 been thrust in from beneath, from rocks which have 

 been laid down from above, as every rock between 

 London and Birmingham or Exeter has been laid down. 

 That I only assert now. But I do not wish you to take 

 it on trust from me. I wish to prove it to you as I go 

 on, or to do what is far better for you : to put you in 

 the way of proving it for yourself, by using your 

 common sense. 



At the risk of seeming prolix, I must say a few more 

 words on this matter. I have special reasons for it. 

 Until I can get you to " let your thoughts play freely" 

 round this question of the superposition of soils and 



D 2 



