

MINERAL VEINS AND ORE-DEPOSITS. • 781 



ment of the Vosges, and at some other localities. They give a good idea of the various 

 reactions which may take place during the filling of a vein, and through subsequent 

 changes in its condition. 



On page 709 mention is made of recent depositions, from hot springs, of quartz crys- 

 tals and chalcedony in layers or crusts. At Clear or Borax Lake, as observed by J. A. 

 Phillips (Quart. J. Geol. Soc, 1879), the siliceous deposits frequently contain pyrite 

 and cinnabar, and the sulphur bank, which has there been formed through the heated 

 vapors, has been worked as a mercury mine. J. D. Whitney reported the occurrence 

 of gold in cinnabar which was supposed to have come from near " Sulphur Springs," 

 four miles south of Bear Valley, between Clear Lake and Colusa; and Mr. M. Atwood 

 has removed the doubt as to the source of the specimen by finding in a fissure at the 

 place mentioned (as reported by Mr. Phillips), cinnabar overlaid by a brilliant deposit 

 of metallic gold. In Nevada, at Steamboat Springs, according to Mr. Phillips, fissures 

 are being lined with a siliceous incrustation, while at the same time steam and gases, 

 (carbonic acid, and sulphuretted hydrogen), with boiling water, are escaping ; and " they 

 have been subjected to a series of repeated widenings," and become lined to a thickness 

 of several feet with silica, which is in bands, amorphous and crystalline alternating, 

 and contains some hematite, pyrite, and chalcopyrite According to Mr. Laur (Ann. 

 des Mines, 1863), the silica of these fissures contains also traces of gold ; so that the facts, 

 as he has stated, exemplify the essential points in the origin of auriferous quartz-veins. 

 This view was presented by B. Silliman and W. P. Blake, in 1864, with reference to 

 the branded quartz veins (gold-bearing) of Bodie Mountain, north of Mono Lake, which 

 fire contact veins intersecting porphyry. 



Further, while the filling of cracks and openings with quartz, making quartz veins, 

 generally results in a very effectual mending of the fractured strata, the introduction of 

 bands of ore and of spars, makes them weak planes in the rock, and weak planes of 

 very great depth and extent. In this latter case, they are liable to be opened anew 

 during subsequent disturbances of the region, and to receive a reheating of the old part 

 and the adjoining rock through the friction occasioned, or rising vapors. Under such 

 circumstances, new material may be introduced to fill the opened spaces, and so add to 

 the number of bands in the vein, and new changes may be set at work among its pre- 

 existing materials. By this means a vein may be doubled or tripled in its bands, and 

 suffer great changes in its ores. The six bands represented in Fig. 1130, are ascribed by 

 De la Beche to several reopenings of the vein ; and of those in Fig. 1131, two or three open- 

 ings seem to be indicated, one for d, one for b, c, b, and perhaps a different one for a. 

 Veins containing no ores often show that they have undergone some disturbing move- 

 ments by the changes in the old minerals in many parts to new silicates or other species. 



The crystals of earlier deposition are often much eroded in the process of change, 

 where not wholly removed. In a small vein in the trap of Mill Rock, near New Haven, 

 Conn., containing prehnite, laumontite, stilbite, quartz, and some traces of copper ores, 

 quartz crystals occur, at times, having the pyramid removed by erosion, and a hexag- 

 onal depression made in its place which is bounded by thin projecting edges of the prism. 

 No flnorids are present ; and nothing is yet known with regard to the eroding agent. 



The existence of veins of ore, which are wholly eruptive, that is, which came up as a 

 melted mass, like dikes of igneous rock, have not been above recognized. Even quartz 

 veins are sometimes described as such; but this mode of origin is at variance with all 

 their characters and with their modes of occurrence, contents, and distribution. It is 

 possible that the native iron, which is found by the ton in Greenland doleryte, may have 

 come in its native state from the deep source of fusion. Doleryte and many other ig- 

 neous rocks contain magnetite, and often also pyrite, in disseminated grains, with traces 

 of native iron, but never enough to make them iron ores. J. Lawrence Smith has sug- 

 gested that the Greenland iron is a result of deoxydation by carbonaceous matters 

 taken into the doleryte while on the ascent to the surface. 



The subject of veins and local ore deposits does not include the ore deposits which 

 are among the earth's strata as part of its stratified rocks. That the true limits of the 

 subject may be understood, the kinds of stratified ore deposits are here enumerated. 



1. Beds of the iron ores, hematite, magnetite, limonite, and siderite (iron carbonate 



