512 



NATURE 



{April i, 1880 



were freely supplied to the geologists and engineers of 

 other countries. The rapid increase of the mines in depth, 

 from 500 to 2,000 feet and upwards during the last few 

 years, has, however, to some extent superseded, or rather 

 rendered a supplement necessary to the earlier accounts, 

 and this is supplied by the volume under consideration. 

 The Comstock lode was discovered in 1859 by some gold 

 miner in a pit sunk for a water-hole, and "milling,'' 

 or reduction of the ore, commenced in the same year, but 

 during the first twelve months the amount of precious 

 metals produced did not exceed 20,000/. in value. Since 

 then it has become the largest gold and silver producing 

 locality in the world, the yield during the nineteen years 

 of its history having been, according to different estimates, 

 from 60,000,000/. to 70,000,000/. in gold and silver. The 

 ore is of two kinds, poor or low grade, averaging in 

 yield from 4/. to 7/. per ton, and rich, worth from 8/. 

 to 22/. per ton. These richer ores occur in large bodies or 

 " bonanzas " recurring at irregular intervals both along the 

 course of the lode and in depth. One of the most remark- 

 able, that of the Consolidated Virginia and California mine, 

 discovered in 1873, at 1,300 feet below the surface, mea- 

 suring 500 feet in depth, 700 feet in length, and 90 feet in 

 thickness, yielded in six years over a million tons of ore, 

 averaging 19/. per ton value. The metal or bullion produced 

 is worth from gs. to iar. per ounce, representing a com- 

 position of about 94 per cent, silver and 6 per cent. gold. 

 The author discusses the various conditions under which 

 these great masses may have been introduced into the 

 lode, distinguishing the periods of eruption of the dif- 

 ferent volcanic rocks forming the walls from the so-called 

 " chemical periods " when the strata of diorite, ande- 

 site, and propylite were attacked by water containing 

 silica and dissolved or disintegrated, the hollows formed 

 being filled up by masses of quartz without metallic 

 minerals of value. Subsequently a great eruption ot 

 trachyte took place, accompanied by movements of the 

 walls of the lode, opening fissures more steeply inclined 

 than those of the first period. These in the " second 

 chemical period " were filled by quartz in the same man- 

 ner as before, but this time accompanied by gold- and 

 silver-bearing minerals, a trace of this action being still 

 recognisable in the hot waters of the Steamboat Springs 

 about twelve miles distant, which, as shown by Mr. J. A. 

 Phillips and others, deposit a siliceous sinter containing 

 at times cinnabar and metallic gold. Or. an extensive 

 study of the various phenomena pre-ented by the distri- 

 bution of the ore bodies both in length and depth, the 

 author, like a true miner, takes a hopeful view of the 

 future, and considers that the prospect of finding a second 

 and lower zone of ore-production within attainable depths 

 is very good. The spirit with which the explorations 

 are followed is best shown by the statement that some 

 half-dozen ^ew vertical shafts are now sinking to cut the 

 lode at depths of 2,500 feet and upwards, one of them 

 being expected to attain a perpendicular depth of 4,500 

 feet. 



Of almost equal interest to the mineral wealth of the 

 Comstock lode are the peculiar heat phenomena observed 

 in the workings, which are very fully described by the author. 

 The air in the lower levels and deep shafts has in places 

 temperatures of from no°to 120 Fah., while the rock and 

 the water pumped from some of the flooded workings at 



times attains 150° and 155°. In one instance 158 was 

 observed in the water of a level at 1,800 feet in depth. 

 The author puts forward the hypothesis that these very 

 high temperatures are due to the kaolinisation of the 

 rock, a large amount of heat being supposed to be evolved 

 by the fixation of water in the production of the great 

 masses of clay which characterise the rocks in the imme- 

 diate vicinity of the lode, and in his own words : "This 

 theory is advanced with confidence in spite of the disad- 

 vantage that no estimate can be made of the specific 

 quantity of heat which is produced by the change men- 

 tioned." Under these circumstances it seems scarcely 

 necessary to discuss the point, more especially as it has 

 been pointed out by Mr. Phillips, in a paper recently read 

 before the Geological Society, that the application of the 

 only available numerical test, namely, comparison of the 

 amount of alkalies in the water pumped from the mines 

 with that contained in the undecomposed rock as a measure 

 of the amount of change, gives such impossible results 

 as to prevent acceptance of the hypothesis in the absence 

 of more positive data. The fact of the boiling springs 

 at Steamboat Springs, twelve miles distant, being 

 diminished considerably in their flow with the increased 

 depth of the mines, while the mine water has become 

 sensibly hotter, would appear to point [to a natural hypo- 

 thesis of common origin in the last or solfataric stage of 

 the phenomena that produced the lode. The volume is 

 illustrated by plans and sections taken from the working 

 surveys of the mines of very great interest and value. 



H. B. 



OUR BOOK SHELF 



Micrometrical Measurements of Double Stars made at 

 the Cincinnati Observatory in 1878 and 1 879, under the 

 Direction of Or/no/id Stone, M.A. (Published by 

 Authority of the Board of Directors of the University, 

 Cincinnati, 1879.) 

 The measurement of position and distances of double 

 stars is perhaps one of the most common researches 

 for which a tele=cope is used, perhaps for the reason that 

 no elaborate apparatus is necessary, and also that almost 

 every one thinks that a double star can be measured 

 without much previous training of the eye. Owing to tin 

 high latitudes of most of the observatories engaged on thi 

 subject, the stars south of the equator are in a great 

 measure neglected compared with those north of it, and 

 in the volume before us we are glad to see that the 

 southern stars from the equator to — 30 have received 

 the greatest attention, some having been measured on 

 twenty or thirty different occasions. Altogether there are 

 2,250 different observations of the 1,054 double stars 

 appearing in the catalogue ; of these 560 are from Struve's 

 catalogue, 171 discovered by the Herschels, 162 by Burn- 

 li.tm, and 85 new discoveries. The results appear to have 

 been corrected with great care and the method of cor- 

 recting observations for errors due to the position of stars 

 relative to the horizon is set forth at considerable length. 

 We notice that all the observations are made with eyes 

 in such a portion that a line joining them would be cither 

 parallel or normal to the line joining the stars, a point 

 that cannot be too much impressed on observers of double 

 stars, since the error often occasioned by neglect of this 

 precaution is surprisingly large. We believe the parellel 

 position to be subject to the last error. 



It seems to be rather a waste of printing to set forth 

 five columns containing position-circle readings ani" 

 assumed zeros, together with the actual readings o 



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