CLOUDS AND RIVERS. ICE AND GLACIERS. 18? 



481. Turn into any well -arranged museum — for 

 example, into the School of Mines in Jermyn Street, and 

 observe the evidence there collected. Look particularly 

 to the fossil trilobites taken from the slate rock. They 

 are in some cases squeezed to one third of their primi- 

 tive thickness. Numerous other specimens show in 

 the most striking manner the flattening out of shells. 



482. To the evidence adduced by Mr. Sharpe, Mr. 

 Sorby added other powerful evidence, founded upon the 

 microscopic examination of slate rock. Taking both 

 into account, the conclusion is irresistible that such 

 rocks have suffered enormous pressure at right angles 

 to the planes of cleavage, exactly as the glacier has 

 demonstrably suffered great pressure at right angles to 

 its planes of lamination. 



483. The association of pressure and cleavage is thu3 

 demonstrated ; but the question arises, do they stand to 

 each other in the relation of cause and effect? The 

 only way of replying to this question is to combine 

 artificially the conditions of nature, and see whether 

 we cannot produce her results . 



484. The substance of slate rocks was once d paistic 

 mud, in which fossils were embedded. Let us imitate 

 the action of pressure upon such mud by employing, 

 instead of it, softened white wax. Placing a ball of the 

 wax between two glass plates, wetted to prevent it from 

 sticking, we apply pressure and flatten out the wax. 



485. The flattened mass is at first too soft to cleave 



