406 BENEFICIAL EFFECTS OF FAULTS. 



many deep and rich mines would have been inaccessible.. 

 (See PI. 65. Fig. 3. and PI. 66. Fig. 2.) Had the strata of 

 Shale and Grit, that alternate with the Coal, been continu- 

 ously united without fracture, the quantity of water that 

 would have' penetrated from the surrounding country, into 

 any considerable excavations that might be made in the po- 

 rous grit beds, would have overcome all power of machi- 

 nery that could profitably be appUed to the drainage of a 

 mine ; whereas by the simple arrangement of a system of 

 Faults, the water is admitted only in such quantities as are 

 within control. Thus the component strata of a Coal field 

 are divided into insulated masses, or sheets of rock, of irre- 

 gular form and area, not one of which is continuous in the 

 same plane over any very large district ; but each is usually 

 separated from its next adjacent mass, by a dam of clay,, 

 impenetrable to water, and filling the fissure produced by 

 the fracture which caused the Fault. (See PI. 66. Fig.. 2... 

 and PI. 1. Figs. I,— 1,1.) 



If we suppose a thick sheet of Ice to be broken into frag-- 

 ments of irregular area, and these fragments again united,, 

 after receiving a slight degree of irregular inclination to the 

 plane of the original sheet, the reunited fragments of ice- 

 will represent the appearance of the component portions of 

 the broken masses, or sheets of Coal measures we are 

 describing. The intervening portions of more recent Ice, by 

 which they are held together, represent the clay and rub- 

 bish that fill the Faults, and form the partition walls that 

 insulate these adjacent portions of strata, which were 

 originally formed, like tlie sheet of Ice, in one continuous, 

 plane. Thus each sheet or incHned table of Coal measures, 

 is enclosed by a system of more or less vertical walls of 



very few instances ascertained ; they are accompanied by a subsidence of the 

 strata on one side of their line, or (whicli amounts to the same thing) an 

 elevation of tliem on the other; so that it appears, tliat the same force which 

 has rent the rocks thus asunder, has caused one side of the fractured mass 

 to rise, or the other to sink. — The fissures are usually filled by clay.'* 

 Geology of England and Wales^ Part I. p<,348. 



