98 SILVER-LEAD DEPOSITS OP EUREKA, NEVADA. 



would be more or less bent. Moreover, water carrying fine particles of 

 ore in suspension, trickling slowly down over an irregularly-inclined sur- 

 face, would not deposit the particles in horizontal layers, but in layers con- 

 forming more or less to the inclination of the bed in which it flowed. This 

 stratification is common enough in the upper part of ore bodies, and is occa- 

 sionally met with in the lower portion, though it is, of course, most apparent 

 when the strata have been least disturbed by pressure. It is not meant 

 that the ore throughout these chambers had a stratified appearance; on the 

 contrary, the different ore-minerals seemed to be mixed throughout the 

 mass without reference to any law of distribution. It sometimes appears 

 as if there were more unaltered galena in the lower portions of ore bodies 

 than in the upper, but the difference, if an)* exists, is so slight that it is not 

 of much importance. In large ore bodies the ore is much more compact 

 at the bottom than at the top, which may be accounted for by the difference 

 of pressure. The limestone surrounding ore chambers is frequently stained 

 with iron. This seems to be less common in the upper part of the caves 

 than it is lower down. The staining of the limestone is often observed 

 where seams are found leading to ore bodies or where separate masses are 

 connected together, as is often the case, by small pipes. 



Evidences in the ore of pseudomorphism after limestone. In many of the Ol'e bodies Which 



have been discovered strong evidence has been found that a portion of the 

 ore is pseudomorphous after limestone, or, in other words, that it has been 

 substituted for that rock. A mass of ore sometimes contains a rounded 

 bowlder of limestone as a nucleus; a great deal of the ore, when it has not 

 been stratified or pressed into a compact mass, exhibits the form of crushed 

 and brecciated limestone. Small masses of ore sometimes completely fill 

 the spaces between the limestone walls; are perfectly solid, and show clearly 

 that they have not been disturbed since they were deposited. If these 

 deposits had been formed by the crystallization of minerals from solution 

 they would have exhibited, notwithstanding their oxidation, the banded 

 structure which is everywhere supposed to be an accompaniment of this 

 manner of deposition. Although the deposits first described are oxidized 

 to a great extent, the change in their chemical nature would not have been 

 sufficient to obliterate all traces of structure from their mass. Pseudo- 



