THE LINEAR FORCE OF GROWING CRYSTALS 287 



ascertained resistance which the crystals offered to crushing 

 stresses. Moreover, there is reason to believe that this area 

 changes constantly as the crystals grow, and is less for a smaller 

 load than for a larger one. 



The upper contact surface of the crystal is also variable, but 

 always much more perfect than the lower. Relatively large 

 areas in perfect contact with the glass plate which supports the 

 weight were frequently found by careful printing. 



Following these determinations, confirmatory experiments 

 were made upon other salts (copper sulphate, ferrocyanide of 

 potassium, lead nitrate), the results being practically the same 

 as those found for alum. 



It is manifest that we here have to do with a force of great 

 geological importance. If quartz, during crystallization, exerts 

 a pressure on the sides of a vein which is of the same order of 

 magnitude as the resistance which it offers to crushing, then 

 this force is also of the same order of magnitude as the resistance 

 of wall-rocks, and it thus becomes possible that, as indicated by 

 observation, the Mother Lode and other great veins have actually 

 been widened to an important extent, perhaps as much as lOO 

 per cent., or even more, by pressure due to this cause. In 

 mining regions the whole country is frequently intersected with 

 systems of quartz veins. Some of these, of course, are of 

 notable size and capable of being worked, provided the quartz 

 is sufficiently rich ; but many more, a number vastly in excess 

 of the large veins, are thin sheets no thicker than a card, in- 

 capable of profitable exploitation by man, though there is little 

 question that these tiny veins have often contributed the bulk of 

 the gold to placer deposits. In such a country there is almost 

 no limit to the effect which might be produced by the force of 

 the growing crystals, and the displacement might readily be so 

 great as to induce important new fissures or important renewed 

 movements on old fissures. 



Again, in a vein where auriferous quartz is being deposited, 

 the growth of crystals may readily extend the space in which 

 successive crops of crystals might grow, so that in certain cases 

 (for instance on an inclined vein, like the Comstock Lode, near 

 the cropping) the deposition of ore might continue almost indefi- 

 nitely and the total deposit thus increase with time. 



