284 BECKER AND DAY 



in some of the deposits of so-called ribbon-ore. In the gold 

 belt of California this term, often used in a different sense, is 

 applied to designate quartzose ores containing thin, parallel 

 lamince of slate. It has often been supposed b}- geologists and 

 mining engineers that the mechanics of this form of deposit 

 consists of a preliminary faulting in the slate, the more or less 

 irregular surfaces of which were forced apart by undulations of 

 or projections from the surfaces of cleavage followed by a quiet 

 deposition of quartz from solution. In some relatively rare 

 cases, however, it can be shown conclusively that the distribu- 

 tion of the slate is not due to faulting. Occasionally the slates 

 contain grit bands which cause a local, sharply marked deflec- 

 tion in the cleavage of the slate ; and in the Mother Lode cases 

 have been observed where such marked laminae have been 

 driven apart normally by some cause or other, leaving room be- 

 tween them for combs of quartz crystals in layers which some- 

 times reach 6 inches in width. When such occurrences cannot 

 be accounted for by faulting, the inference is almost unavoid- 

 able that the lamince have been driven apart by the force of the 

 growing crystals, the axes of which stand sensibly at right 

 angles to the planes of the laminae. This hvpothesis, however, 

 ought not to be accepted without the most careful scrutiny, for it 

 implies force of great intensity. If the lamina? have been forced 

 apart in this way, then the whole lode must have been increased 

 in width by the same means ; and when the sum of the dis- 

 tances between the slate bands is taken into consideration, this 

 indicates a force of orogenic intensitv and of really stupendous 

 aggregate amount. The Mother Lode in California is some- 

 thing like 150 miles in length, and has been explored to a depth 

 of several thousand feet. Its width is often several hundred 

 feet, and that such a cleft could have been opened or consider- 

 ablv increased in width through the force of growing crystals 

 is certainly hard to believe. 



Experiments on the subject were instituted immediateh' after 

 the first observation of this kind was made. The first effort 

 was directed to ascertaining whether crystals of a substance like 

 alum would raise a glass jtlate bencatli whicli a saturated solu- 

 tion of the salt had been introduced. The experiment was im- 



