EXDUCE.l GEOLOGY FOSMATION OF VEUSS AND LODES. 279 



ever, -what kind of infiltration is usually employed in filling these fis- 

 sures. Numerous hypotheses have been offered in explanation, favoring 

 infiltration from above, below, from the side, &c. ; but the reliable data 

 obtained are too few as yet to admit of any well-grounded view. One fact 

 has been elicited, however, the cause of which is obvious, and may event- 

 ually lead in the right direction towards solving the problem. In a large 

 number of instances it has been noticed that the filled fissure, the lode, 

 showed a symmetrical arrangement of its component minerals, so that 

 by dividing it into two halves, parallel to the walls, these halves would 

 each contain the same minerals in the same consecutive order. This 

 structure has been termed "combed," and leaves no doubt that the same 

 minerals, at their corresponding positions, were deposited contempora- 

 neously, and that the filling must have progressed from the walls inward, 

 i. e., to the center of the fissure. The why and wherefore cannot yet be 

 answered satisfactorily. 



Attempts have been made to explain the filling of fissures by the 

 action of electric currents ; but it seems more probable that those cur- 

 rents, which really do exist in lodes, are not the cause, but the result 

 of their formation. 



SEASCH FOE LODES. 



In searching for lodes, it is undoubtedly best to simply follow the 

 teachiug of scnnd judgment, combined with empirical and other knowl- 

 edge. 



Should the gangue-rock be harder than the surrounding " country," 

 offer more resistance to atmospheric influences, the aspect of a hill or 

 ridge will often reveal the desired point at a glance. Apart from «this 

 very convenient method of prospecting, inquiry should always be made 

 whether at any time mining ©iterations had been carried on in the dis- 

 trict being prospected; if so, the strike of the lodes then discovered — '■ 

 if ascertainable — will always afford a valuable hint to the prospecter. 

 If it is an entirely new country to mining-industry, the experience 

 gained upon former occasions must be applied to decide whether it may 

 look '-promising" or not. Valuable and time-saving is the custom of 

 examining the sand of rivers and creeks, because any mineral found in 

 this sand must necessarily occur exposed at some point above the one 

 where it was first observed. Not having obtained any satisfactory 

 results from this process, an examination of the rocks in position, as far 

 as they are exposed, can be undertaken. The color of the soil must be 

 observed, if possible, as sulphurets an,diron ores mostly produce a red; 

 copper compounds, a greenish color. Vegetation is an important indi- 

 cator for the prospecter. If it is particularly luxuriant along certain 

 limited areas, or the reverse, it may lead to valuable discoveries. In 

 prospecting for salt and -similar compounds, the character of the vegeta- 

 tion is of the greatest aid. 



After having found any mineral that may have the appearance of an 

 ore, it becomes necessary to recognize its nature, and, if it is decomposed, 

 the nature of that from which it resulted. An old plan in prospecting 

 a country where veins are supposed to exist is to start from any point 

 where a piece of ore has been found in two directions at right angles 

 with each other, whereby every lode within the one-half of the circle will 

 be crossed. In a country where mining has been, or is still, carried on, 

 it will be of use to make the examination while traveling at a right 

 angle to the usual strike of the lodes. 



When the presence of the lode has been established, it must be fol- 

 lowed up, and here frequently the skill of the prospecter is subjected to 



