PRINCIPLES CONTROLLING ORE DEPOSITS 749 



and finally die out altogether. Water in a fissure may descend 

 or may ascend for a considerable distance ; but it is perfectly 

 clear that, so far as fissures are concerned, except for the small 

 amount entering the surface openings, the water must enter 

 laterally. Consequently, if we apply the lateral-secretion theory 

 broadly enough, we may say that all the waters which feed the 

 fissures are lateral-secreting waters. But if we are descension- 

 ists, and consider only the upper part of a fissure on the slope — 

 and that is what many very naturally have done because this is 

 the part of the fissure most easily observed — we may say that 

 the waters which are doing the work are descending waters. 

 Or, if we are in such a district as that of the Comstock lode, in 

 which are found great volumes of ascending water, we may say 

 that the waters which are depositing the ores are ascending. 

 All may be true. But in the past Sandberger held that lateral- 

 secreting waters in the narrowest sense did all the work, and he 

 refused to believe that ascending and descending waters were of 

 importance ; and Posepny held that ascending waters did nearly 

 all the work, and gave small consideration to lateral-secreting 

 and descending waters ; whereas you see with perfect clearness 

 that each theory is incomplete. Both are needed ; they supple- 

 ment each other. 



Passing now to the work of underground water, we find there 

 are very great differences in the nature of the work which takes 

 place above the level of groundwater and below the level of 

 groundwater. The first is called the belt of weathering; the 

 second the belt of cementation 1 (see Fig. 7). Also there are 

 great differences in the work which takes place in the zone of 

 fracture, which includes both the belts of weathering and cemen- 

 tation, and that in the deep-lying zone, that of rock flowage. 

 All of these differences have a very close bearing upon some 

 phase of ore deposition. But the subject is too complex for me 

 to take up fully, and I shall simply give the major differ- 

 ences in the reactions without stopping to demonstrate their 



1 Metamorphism of Rocks and Rock Flowage, by C. R. Van Hise : Bull. Geol. 

 Soc. Am., Vol. IX, p. 278. 



