62 



FAULTS. 

 Fig. 85. 



[Oh. V 



A^- ^-£L 



13 3> 



Faults. A B perpendicular, D oblique to the horizon. 



ttie strata on each side of the faults A B, CD, continue parallel to one 

 another ; in other cases, the strata on each side are inclined, as in a, 6, c, d 



Fig. 86. 



f d c h a 



E F, fault or fissure filled with rubbish, on each side of which the shifted 

 strata are not parallel. 



(fig. 86), though their identity is still to be recognized by their possessing 

 the same thickness, and the same internal characters."* 



In Coalbrook Dale, says Mr. Prestwich,f deposits of sandstone, shale, 

 and coal, several thousand feet thick, and occupying an area of many 

 miles, have been shivered into fragments, and the broken remnants have 

 been placed in very discordant positions, often at levels differing several 

 hundred feet from each other. The sides of the faults, when perpendicu- 

 lar, are commonly separated several yards, but are sometimes as much 

 as 50 yards asunder, the interval being filled with broken debris of the 

 strata. In following the course of the same fault, it is 'sometimes found 

 to produce in different places very unequal changes of level, the amount 

 of shift being in one place 300, and in another 700 feet, which arises, in 

 some cases, from ;he union of two or more faults. In other words, the 

 disjointed strata have in certain districts been subjected to renewed move- 

 ments, which they have not suffered elsewhere. 



We may occasionally see exact counterparts of these slips, on a small 

 scale, in pits of loose sand and gravel, many of which have doubtless 

 been caused by the drying and shrinking of argillaceous and other beds ? 

 slight subsidences having taken place from failure of support. Sometimes, 

 however, even these small slips may have been produced during earth- 

 quakes ; for land has been moved, and its level, relatively to the sea, 

 considerably altered, within the period when much of the alluvial sand 

 and gravel now covering the surface of continents was deposited. 



* Playfair, Ilhist. of Hutt. Theory, § 42. 

 f Geol. Trans, second series, vol. v. p. 452. 



