GEOLOGICAL PAPERS. 1 3 t 



number of blanks were greater than the number which showed values, 

 but the shales were taken from all parts of the formations, and many 

 of them doubtless contained no gold. Since then I have made many 

 luindreds of assays, and I suppose the average values obtained are two 

 dollars or three dollars a ton. 



One series of sixty-six assays made last summer gave an average of 

 $2.58 per ton. In my laboratory, recently, by concentration methods, 

 144 assays gave an average of $13.52 per ton. This last series of assays 

 was joint work of several persons, all of whom were solicitous to find 

 the exact truth, and there was no intentional error ; but in work divided 

 among several people, no one can be absolutely certain. 



Last July Mr. F. H. Blake, of New York, obtained samples of shale, 

 and had twenty-five assays made from as many different specimens by 

 Mr, Henry E. Wood, of Denver. Six of these showed no gold, ten 

 showed traces, and nine gave values ranging from twenty cents to six- 

 teen dollars a ton. 



In my laboratory last week, Mr. S. B. Edwards, a chemist of Colo- 

 rado, made nineteen assays and obtained an average of $2.08 per ton. 

 His highest value was $18.78, and the lowest forty-two cents per ton. 

 His work was done on thirteen specimens collected from the shale 

 banks by himself. I might multiply assay records of this kind, but I 

 have given a fair sample of those which have come to my notice. The 

 most puzzling part of the investigation is that from the same pulp, 

 mixed as carefully as we know how to do it, very discordant values 

 will appear. They have varied as much as fifty dollars per ton, 



I have but two hypotheses to account for this discordance. The- 

 first is that the gold is not uniformly distributed, and that unwittingly, 

 in taking our assay, we get a rich portion one time and a lean portion 

 another. This may be true, but to one knowing the care taken in 

 mixing the ore it does not seem likely, and is contrary to the experi- 

 ence of those who sample ore for commercial purposes. The other 

 hypothesis is that, owing to the unknown and peculiar conditions of 

 the ore, very likely to its fine divisions, the values in one case are led 

 away by heavy vapors, while in another instance the values are in 

 some way retained. 



It may be suggested that fraud has been perpetrated in getting 

 these results, and even if the assay is honest, others, less scrupulous, 

 have had a share in the work. But the same experience has fallen to 

 quite a number of assayers who are working with the greatest circum- 

 spection on specimens taken by themselves from the shale-beds. 



There are other methods of analysis besides fire assays that I have 

 tried on shales. My experiment with the chlorination process met 

 with the following difficulty: The ore was roasted with sodium chlo- 



