86 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



ferric oxide, is usually the richest. There are several exceptions to be 

 noticed in these specimens, but they do not seem to be sufficient to affect 

 these general results. Although it has not been possible to fix with cer- 

 tainty on any particular variety of limestone which is to be regarded as 

 the poorest, or richest, its contents in the precious metals bearing no very 

 definite relations to its physical properties, yet it is usually possible to form 

 some idea of the value of a piece of rock from its appearance, the crushed 

 and stained varieties being usually the richest. It will be noticed that the 

 specimens taken on either of the lines leading up to their junction below 

 the large ore bodies do not show a gradual increase in value as the ore is 

 approached. The want, of regularity in this increase is owing to the facts 

 that there is no uniformity in the character of the limestone, and that there 

 appear to be zones of rich and poor rock crossing the course of the main 

 drift and cross-drift. The existence of such zones cannot be fully estab- 

 lished by the number of assays that were made, as the limestone is con- 

 stantly changing, and a rich piece and a poor piece are often found side by 

 side; still the variations of certain groups of assays from the general aver- 

 age indicate that such zones exist. 



Sample No. 3, in the first list of assays on the main drift, shows 34 

 cents in silver. This is an extraordinary amount to be obtained from lime- 

 stone within the stratified zone, but although other samples were taken 

 from the same spot no second such assay was obtained. It is abnormal, 

 and it would have been struck from the list had it not been deemed proper 

 to give the assays exactly as they were taken, although in reckoning the 

 average assay value of the stratified limestone (Nos. 2, 4, 5, 6, 7, and 8) it 

 has been omitted, as the other samples which were taken afterwards in the 

 same spot were less than the average (121 cents). 



The average of the next five samples, from 9 to 13 inclusive, which 

 were taken from the crushed limestone, is 15i cents. The stratified and 

 crushed limestones are separated by a fissure which may have been the 

 source of impregnation of the zones on each side of it. At any rate the 

 averages of five samples decrease down to the fourth lot assaying 101, when 

 they begin to increase again up to No. 34, which is in the next zone of 

 stratified limestone. The average value of this zone of stratified limestone 



