Chap. 45.] trapping of Strata. 19$ 



vitrifiable fand mixed with foflll fhells, two of fine gra- 

 vel, three of ftony marie, one of coarfe powdered 

 marie, one of ftone, calcinable like marble, three of 

 grey fand, two of white fand, one of red fand ftreak'ed 

 with white, eight of grey fand with fhells, three of very 

 fine fand; three of a hard grey ftone, four of red fand 

 ftreaked with white, three of white fand, and fifteen of 

 reddiih vitrifiable fand.' 



The direction too in which the ftrata are found 

 is alfo exceedingly different in different fixations. 

 * When the continuity,' fays Mr. Jones, c of the ftrata 

 is interrupted by a fracture, the ftrata are thrown out: 

 of that horizontal pofition which is natural to them, 

 and make an angle with the horizon ; which may be 

 called the angle of their elevation or depreffion ; the 

 miners call it their dip. In this cafe, if the fuccefiion 

 of ftrata is accurately noted on one fide of the fracture, 

 where a vein of coal or metal is found amongft them, 

 it may thence be learned where the fame vein will 

 occur again on the other fide of the fracture ; becaufe^ 

 it will be found adjacent to the fame ftrata as before. 

 When the edges of the ftrata, on each fide of a fiffure, 

 are thus parted and mifmatched, they are faid to trap-, 

 and the fpace between them is filled up with rubble, 

 or ftones, or minerals, &c. Sometimes thefc fiffures 

 are the richeft parts of the foil, containing fuch matters 

 as are not to be found elfewhere *. In fig. I. plate I. 



F. repre- 



* Some of the fiffures in Cornwall are near twenty feet over, 

 and commonly full, or near it, of metallic and mineral matter. 

 The fiflurcs at the greateft depth are generally largeft ; as we af- 

 cend they become gradually lefs, but more frequent and nu- 

 merous : infomuch that if the globe was divided, in two., and the 

 ftrata viewed upon the face of the fedlion, the figures would ap- 

 pear after the manner of a tree: at the bottom a large trunk, 

 which higher up is divided into branches, which break into lefler, 

 U 3 and 



