770 ORIGIN OF METALLIFEROUS VEINS. [Ch. XXXVIIL 



accompanied by a displacement of the rocks along the plane of 6 b. 

 This new opening was then filled with minerals, some of them re- 

 sembling those in a a, as fluor-spar (or fluate of lime) and quartz; 

 others different, the copper being plentiful and the tin wanting or very- 

 scarce. 



We must next suppose the shock of a third earthquake to occur, 

 breaking asunder all the rocks along the line c c, fig. 763 ; the fissure, 

 in this instance, being only 6 inches wide, and simply filled with clay, 

 derived, probably, from the friction of the walls of the rent, or partly, 

 perhaps, washed in from above. This new movement has heaved the 

 rock in such a manner as to interrupt the continuity of the copper 

 vein (b b), and, at the same time, to shift or heave laterally in the 

 same direction a portion of the tin vein which had not previously been 

 broken. 



Again, in fig. 764, we see evidence of a fourth fissure (d d), also filled 

 with clay, which has cut through the tin vein (a a), and has lifted it 

 slightly upwards towards the south. The various changes here repre- 

 sented are not ideal, but are exhibited in a section obtained in work- 

 ing an old Cornish mine, long since abandoned, in the parish of Red- 

 ruth, called Huel Peever, and described both by Mr. Williams and 

 Mr. Carne.* The principal movement here referred to, or that of 

 c c, fig. 764, extends through a space of no less than 84 feet ; but in 

 this, as in the case of the other three, it will be seen that ,fche outline 

 of the country above, c?, c, 6, a, &c, or the geographical features of 

 Cornwall, are not affected by any of the dislocations, a powerful de- 

 nuding force having clearly been exerted subsequently to all the faults. 

 (See above, p. 69.) It is commonly said in Cornwall, that there are 

 eight distinct systems of veins which can in like manner be referred 

 to as many successive movements or fractures ; and the German miners 

 of the Hartz Mountains speak also of eight systems of veins, referable 

 to as many periods. 



Besides the proofs of mechanical action already explained, the 

 opposite walls of veins are often beautifully polished, as if glazed, and 

 are not unfrequently striated or scored with parallel furrows and 

 ridges, such as would be produced by the continued rubbing together 

 of surfaces of unequal hardness. These smoothed surfaces resemble 

 the rocky floor over which a glacier has passed (see fig., p. 140). 

 They are common even in cases where there has been no shift, and 

 occur equally in non-metalliferous fissures. They are called by miners 

 " slicken-sides," from the German schlickten, to plane, and seite, side. 

 It is supposed that the lines of the striae indicate the direction in 

 which the rocks were moved. During one of the minor earthquakes 

 in Chili, which happened about the year 1840, and was described to 

 me by an eye-witness, the brick walls of a building were rent vertically 

 in several places, and made to vibrate for several minutes during each 



* Geo!. Trans., vol. iv. p. 139 ; Trans. Roy. Geol. Soc, Cornwall, vol. ii. p. 90. 



