Cu. VI] 



OF STRATIFIED ROCKS. 



69 



curacy. Thus in the coal field of Ashby de la Zouch, in Leicestershire 

 (see fig. 91), a fault occurs, on one side of which the coal beds ah c d 



Kg. 91. 



/; 



-"d" 



r^' 



.- — 



ir'c" 



7v ^^""^Ih- 



6 



— ^'P= 



T 



C 



r 



' 



— s — // 



Faults and denuded coal strata, Ashby de la Zoucb. (Mammat.) 



rise to the height of 500 feet above the corresponding beds on the other 

 side. But the uphfted strata do not stand up 500 feet above the general 

 surface ; on the contrary, the outline of the country, as expressed by the 

 line z 0, is uniformly undulating without any break, and the mass indicated 

 by the dotted outline must have been washed away.'* There are proofs 

 of this kind in some level countries, where dense masses of strata have 

 been cleared away from areas several hundred square miles in extent. 



In the Newcastle coal district it is ascertained that faults occur in 

 which the upward or downward movement could not have been less than 

 140 fathoms, which, had they affected the configuration of the surface to 

 an equal amount, would produce mountains with precipitous escarpments 

 nearly 1000 feet high, or chasms of the like depth ; yet is the actual level 

 of the country absolutely uniform, afibrding no trace whatever of subter- 

 ranean movements.! 



The ground from which these materials have been removed is usually 

 overspread with heaps of sand and gravel, formed out of the ruins of 

 the very rocks which have disappeared. Thus, in the districts above re- 

 ferred to, they consist of rounded and angular fragments of hard sand- 

 stone, limestone, and ironstone, with a small quantity of the more 

 destructible shale, and even rounded pieces of coal. 



Allusion has been already made to the shattered state and discordant 

 position of the carboniferous strata in Coalbrook Dale (p. 62). The 

 collier cannot proceed three or four yards without meeting with small 

 slips, and from time to time he encounters faults of considerable magni- 

 tude, which have thrown the rocks up or down several hundred feet. 

 Yet the superficial inequalities to which these dislocated masses origi- 

 nally gave rise are no longer discernible, and the comparative flatness of 

 the existing surface can only be explained, as Mr. Prestwich has observed, 

 by supposing the fractured portions to have been removed by water. It 

 is also clear that strata of red sandstone, more than 1000 feet thick, 

 which once covered the coal, in the same region, have been carried away 



* See Mammat's Geological Facts, (fee, p. 90, and plate, 

 f Conybeare's Report to Brit. Assoc. 1842, p. 38 L 



