Vol. 65.] GEOLOGICAL FEATURES OF CARPALLA CHINA-CLAY PIT. 157 



Fault. 



it is also soon lost as it passes down into the china-clay rock of the 



great pit. 



The actual amount of down- 

 throw cannot at present he 

 determined ; the pits along 

 the west side of the railway 

 and the great china-clay ex- 

 cavation itself expose more 

 than 50 feet of schist ; whence 

 it may he inferred that there 

 has been a downthrow of at 

 least that amount. Ordinarily 

 the fault-fissure is only a few 

 inches wide, and is tilled 

 with loose material derived 

 from the walls thereof; but 

 occasionally the filling has 

 been indurated by secondary 

 developments of schorl and 

 quartz, when the two rocks 

 may be seen in juxtaposition. 

 The tourmaline-schist, other- 

 wise lying almost horizontally, 

 is much contorted near the 

 fault. In some places near 

 the fault numerous secondary 

 veinlets of quartz and schorl 

 occur ; but farther away the 

 schist is quite free from con- 

 tortion and veining. Some 

 30 years ago, when the clay- 

 pit was less than half its 

 present depth, the faulted 

 schist or killas appeared as an 

 almost upright wall bounding 

 its southern side, as shown 

 in the section (fig. 2). On 

 working the clay to a greater 

 depth, it has been found to 

 extend southwards beneath 

 the killas for many fathoms. 



The recent investigations 

 have shown that this killas is 

 a nearly isolated patch, as in- 

 dicated on the accompanying 

 plan. (fig. 1, p. 156), having 

 a thickness near corner A of 

 40 to 50 feet, thinning off' at 

 corners B & C, covered every- 

 where by growan, and resting upon china-clay rock, which is in 

 all respects similar to that exposed in the great clay-pit. 



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