PROCEEDINGS OF THE COTTESWOLD CLUB 243 



These lenses or lenticles are of all sizes, from the dimen- 

 sions of a sofa-cushion down to the minuteness of a wafer. 

 In the granite, which is a very coarse rock, they are much 

 thicker in the middle than they are in the finer-grained 

 varieties of diorite, where they are almost like uniform 

 sheets, though of course they thin out towards the 

 margin. 



The bands of rock within which shearing and sliding 

 have taken place, I have called " shear-zones." These 

 zones vary in breadth between a few lines, or inches, and 

 several yards, or hundreds of yards. They usually strike 

 obliquely across the axis of the hills, and their laminated 

 structure gave rise to the belief that they were composed 

 of aqueous sediments subsequently metamorphosed by 

 heat. This hypothesis, I may remark, was at the time, a 

 very natural one, since deposition under water was the 

 only cause known to the older geologists which was 

 capable of producing a laminated or banded structure. 



I need hardly point out that all this crushing and shear- 

 ing must have been attended with the evolution of heat. 

 The rubbing of two sticks against each other will cause 

 heat enough to kindle the wood. What then must have 

 been the result of the friction between flakes of sohd 

 rock, forced to slide over each other under inconceivable 

 earth-pressures ? An illustration taken from modern 

 engineering will throw some light on the problem. 



Dr. J. W. Redway, of Mount Vernon, New York, 

 writing in " Science," in 1894,^^ describes a remarkable 

 accident that happened to some machinery. A cone- 

 shaped bearing was found to be too large for the cylindrical 

 box in which it was supposed to revolve. Dr. Redway 

 goes on to say : " A speculative workman thought it might 

 " wear down to shape, and started the machinery. The 

 " experiment, though of doubtful success from a mechanical 



* Feb. 9, p. 79. 



