Page:Popular Science Monthly Volume 55.djvu/319

Rh difficult to gauge by the standard of the mercurial index. I shall not hazard a guess as to the actual reading.

Taking the mountains in their entirety, it is difficult from single points of view to determine for them any definite relation. There are so many valleys in close proximity to one another, some very ancient and others relatively modern, and with trends so opposed in all directions, that in the absence of a dominant ridge or mass this relation becomes very confused; and I was not in a position, with the limited time at my command and the deficiency of rock outcrops, to positively define any main line or axis of uplifts. Yet I suspect that there is one such, with a generally east and west bearing, whose trend might correspond with that of the ridge already referred to, which, with a southwesterly deflection, unites Dome Mountain with the mass that separates the upper Eldorado from Chief Gulch. What strikes one as particularly interesting in the conformation of some of these mountains when seen from an elevation is their hummocky appearance. This is particularly noticeable in the mountains which close in the Eldorado and Bonanza Valleys. With considerable actual elevations, they convey the impression of being merely swells or undulations of an open surface, very much like magnified morainic knolls in a glaciated country. This depressed type of mountain structure, with the evidence of its expanded valleys and gently flowing contours, carries with it the proof of long-continued degradation, and of a history whose pages read far back into geological chronology.

With the evidences of antiquity before us, there are yet indications, amounting, it seems to me, almost to proof, that many of the more pronounced features of the region date their origin from only a comparatively recent period. Such is the case with a number of valleys that are tributary to the main ones, and even the latter appear to have been modified by late stream displacements. Taking the Eldorado or Bonanza, with their open U-shaped troughs and in most parts gently sloping banks, as types of the older valleys, it is surprising to note how many of their tributaries have the deeply incised and narrow contours; and I am led almost to conclude that some of these are really of very late construction. The stream displacements, which, by reason of the indices they give to the finding of new placers, are now beginning to be so attentively studied by the miner and prospector, are emphatic in their testimony in this direction. One has but to note the triangular area that is included