132 



GEOLOGY. 



large blocks of it have been know r n gradually to bend 

 very considerably. Kane saw this in a flat block of ice 

 eight feet thick, and twenty or more wide, supported 

 only at its two ends. In the course of two months it 

 became so much bent that the middle of it was depressed 

 five feet. 



215. How the Flexures are Produced. It is supposed 

 that the flexures of the strata were produced by lateral 

 pressure. This has been illustrated by a simple experi- 

 ment by Sir James Hall. He took 

 pieces of cloth, some linen and some 

 woolen, and, placing them in layers on 

 a table (Fig. 53), compressed them by 

 the weight a. He then applied press- 

 ure to the sides b #, 

 as shown in Fig. 54, 

 and found that while 

 the weight a was 

 raised, the layers of cloth were bent 

 in folds like those which are seen in 

 layers of rock in nature. Sir C. Lyell 

 observed a result near Boston which 

 well illustrates the action of this later- 

 al pressure. For the purpose of con- 



Fig. 54. 



verting part of an estuary, overflowed at high tide, into 

 dry land, a vast quantity of stones and sand was thrown 

 into it. The effect of this was to push up the bottom 

 of the estuary alongside of this load of stones and sand, 

 so that it, in the course of a few months, was raised 

 six feet above high-water mark, and some five or six 

 folds were produced in it, just like the folds, small and 

 great, which the geologist finds in rocky strata. 



216. Upheavals of Strata, with Fracture. Fig. 55 is a 



Fig. 55. 



