J. Le Conte

On the origin of normal faults and of the structure of the Basin region

I HAVE already, in a previous paper (Am. Geol., vol. iv, p. 38), gi ven reasons for thinking that the general structure of the earth is that of a solid nucle,us constituting nearly its whole mass, a solid crust of inconsidprable comparative thickness, and a subcrust liquid layer, either universal or over large areas, separating the one from the other. In this paper I assume such a general constitution. I assume also that the crust rests upon the su bcrust liquid as a floating body. We may well assume this because, broken as we know the crust to be, if it were not so it would long ago have sunk into the subcrust liquid. I have also, in the previous article already alluded to, shown that this condition of flotation would be the necessary result of the increasing density of the earth as we go down. I now wish to apply these two assumptions to the explanation of Normal Faults and of the origin of the Structure of the Basin region. Crust-jis8ure8 and great faults.-Leaving aside the small fractures called joints which affect rocks of all kinds and in all places, the crust of the earth, as is well known, is everywhere traversed by great fissures more or less parallel to one another in the same region, often hundreds of miles in length, and passing entirely through the crust into the subcrnst liqnid beneath, by which the crust is broken into great oblong crnst-blocks many miles in extent and through which the subcrust liquid is often outpoured on the surface in the form of lava sheets. The walls of such fissures do not remain in their original position but are always slipped, one side being heaved and the other dropped_

On the genesis of metalliferous veins

THE phenomena of metalliferous deposit by solfataric actionat Sulphur Bank and Steamboat Springs have tended strongly to confirm what I had previously believed to be the most prob· able theory of vein-formation, and at the same time to give it more clearness and definiteness. This paper, therefore, may he regarded as a continuation and development of the thoughts started in the previous ones.* The structure, the mode of occurrence and the contents of metalliferous veins leave no longer any room for doubt that they have been formed by deposit from solutions. If any doubt still lingered on this subject, they are now dissipated bv the phenomena of deposit still in progress at Sulphur Bank and at Steamboat Springs. Among metallic ores cinnabar has long been considered a possible exception to this mode of deposit. The extreme volatility of this sulphide, the extreme irregularity of its veins, and its frequent occurrence in the immediate vicinity.of comparatively recent volcanic action, have suggested that it may have been deposited in irregular fissures, cracks, cavities, etc., by condensation of its vapors, sublimed by. vol· canic heat beneath. But the phenomena of Sulphur Bank and Steamboat Springs ought to settle this question forever. Cill-

On the great lava-flood of the West; and on the structure and age of the Cascade mountains

DURING the past summer, I made a geological tour through portions of central and eastern Oregon, the principal object of which was to examine the great lava-flood which covers this region, and more especially to study the structure and determine the age of the Cascade Mountains. In this tour I was accompanied and greatly assisted by Rev. Mr. Condon of the Dalles, a man widely known and greatly honored, no less for his disinterested courtesy than for his extensive knowledge of the geology of this portion of the State. Two years before, I went over nearly the same ground, and also extended my observations into Washington and British Columbia. The pur~ose of my last visit was to solve, if possible, some of the questIOns started in the first visit.