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REVIEW AND GENERAL DISCUSSION. 



517 



if this statement merely referred to the value of the crude gold before melting, it might easily be 

 due to the fact that large pieces of gold are liable to contain a higher percentage of bits of quartz 

 or other rocky matter than are the liner particles. But it refers to a very different tiling. The 

 gold is not assayed at all until after melting. And the fact as stated is, that the coarser gold 

 actually contains on the average a higher percentage by weight of silver than the finer gold does. 

 I know of no explanation of this, and simply mention it as an interesting and curious fact, whose 

 significance remains to be studied hereafter. 



I will also note here, though it be a repetition, the fact that among all the hydraulic mines I 

 visited, and all the miles of tunnels and drifts, etc., that I traversed in 1871, I never yet saw a 

 spot where the bed-rock was exposed in these mines, and was hard enough to show anything of 

 its original surface, where it did not exhibit unmistakably the wearing and smoothing effects of 

 water. Whether the rock were high or low, it was always water-worn. In fact, the water seems 

 to have run at one period or another over almost if not quite every square foot of the bed-rock 

 that now lies buried under either the gravel or the volcanic matter. 



I may as well say here a few words upon the forms of the depressions and furrowings in the 

 water-worn bed-rock, and the extent to which they may be relied upon as indications of the direc- 

 tion of flow of the water over it. Both Mr. Pettee and Mr. Bowman called my attention to these 

 things before I started out in the spring of 1871, and if I understood them aright, they were 

 then inclined to place considerable reliance upon a peculiar and not uncommon form of depression, 

 which Mr. Pettee once not inaptly characterized as slipper-shaped, that is, an elongated depression 

 or trough, with a steep descent at one end and a gradual rise towards the other. I then under- 

 stood that wherever these slipper-shaped depressions were numerous, their steeper ends were 

 almost all turned in the same direction ; and the question was : In such cases did the water flow 

 in the direction of the less steep slope, or vice versa? I do not know whether they were satisfied 

 upon this point or not ; but I afterwards paid particular attention to these depressions at Iowa 



Hill, and numerous other localities, and though I could find plenty of the slipper-shaped depres- 

 sions, yet I could never find any uniformity in the directions towards which their steeper ends 

 were turned. There was often, indeed, a general approach to parallelism in the directions of the 

 axes of the elongated depressions, whatever might be the forms of their ends ; but if, for ex- 

 ample, tin 1 , direction of the axes was northeast and southwest (which is the commonest direction), 

 it generally happened that some of the slipper-shaped depressions had their northeast ends the 

 steepest, and some the southwest ends, and I could never tell, at any one locality, which of these 

 two were the most numerous. My conclusion therefore was that the shape of the ends of the 

 depressions was of no special value as an indication of the direction of the flow. 



Moreover, I did not find well-defined slipper-shaped depressions by any means the most com- 

 mon form. So far as my own observations went, the most common form of depression, and the 

 only one which seemed to me anything like a regular and uniformly intelligible result of the 

 direct action of the water, was a simple furrow. In various localities these little furrows were very 

 numerous. They vary in length from a foot or less to eight or ten feet, and in width and depth 

 from two or three inches to a foot, the width, however, being generally considerably greater than 

 the depth. They are not often either exactly straight or regular. But their little irregularities 

 are always smoothed and rounded, and there is generally a tolerable approach to parallelism in the 

 average directions of their axes. There is no regularity to be traced in the forms of their ends so 

 far as I could see. Where I first noticed these little furrows they were mostly very nearly parallel 

 with the strike of the slates, and I had of course a suspicion that the bedding of the rock might 



have had something to do with their origin. 



But I afterwards found them almost at right angles 



with the stratification, and at other localities crossing it obliquely, and still preserving their general 

 parallelism and characteristic appearance, and I therefore concluded that they were really due to 

 the action of the water in such a way as to be indicative of the direction of its flow. I afterwards 

 noticed the same thing in the bed of the present Dry Creek, below the village of Amador City. I 

 think that where these little furrowings are numerous, it is safe to infer that the water flowed in 



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