6o2 



NA TURE 



[April 19, 1900 



The mines of Aspen were mainly discovered and opened by 

 men whose most recent mining experience had been at Lead- 

 ville, where the silver-ores were found principally at or near the 

 contact of limestone, with overlying sheets of porphyry. The 

 ores consist chiefly of lead and zinc sulphides, carrying silver, 

 with a gangue of barytes, quartz and dolomite. Rich shoots of 

 ore occur chiefly at the intersection of two or more faults, and 

 the theory is advanced that while the minerals were deposited by 

 hot waters, the solutions ascending along one of these channels 

 were precipitated by solutions which circulated along the other. 



The fundamental rock in the district is a granite, and this is 

 overlaid by Cambrian, Silurian, Devonian, Carboniferous, Jura- 

 trias and Cretaceous. The Cambrian and Silurian formations 

 are comparatively thin, and they consist largely of dolomitic 

 sandstones and shales. The Devonian beds, which are very 

 variable in character, comprise limestones and calciferous sand- 

 stones of no great thickness, and they are characterised by the 

 presence of fishes of Devonian type. The Carboniferous and 

 also the Secondary formations attain a great thickness. Into 

 these strata, probably in Cretaceous times, there were intruded 

 dykes of quartz-porphyry and diorite-porphyry. Great physical 

 disturbances took place, accompanied by distinct systems of 

 faults, some developed before, others after the deposition of the 

 ©res. In the author's opinion some faults have developed 

 almost entirely in Post-Glacial times, the evidence resting partly 

 on the preservation of scarps with slickensided fault-surfaces. He 

 believes also that in many cases the fault-movement is going on 

 at the present day. Since the beginning of the great disturb- 

 ances, about 15,000 feet of sedimentary rocks have been removed 

 by denudation ; in later times by glacial action. A general ice- 

 sheet at one time covered the whole of the Aspen district, 

 leaving evidence of its presence in the rounded and fluted forms 

 into which the hill-tops are carved, and in deposits of morainic 

 material. When the ice-sheet shrank to smaller dimensions, 

 there resulted local glaciers which followed the course of pie- 

 existing valleys, and carved them into their present forms. At 

 this period temporary lakes were formed by the damming up of 

 glacial waters. 



The author has given considerable attention to the subject of 

 dolomitisation. He remarks that along the channels afforded 

 by faults, hot spring-waters containing carbonate of magnesia 

 rose and produced the dolomitisation of the limestone. Zones 

 in the limestone following watercourses which are parallel to 

 the bedding, or which cut across it, are locally altered to dolo- 

 mite. There is evidence also of an earlier period of such chemical 

 interchange, some of the Silurian and Carboniferous sediments 

 having been early converted into dolomite by the action of 

 magnesium salts contained in the waters of a great lake or 

 inland sea, and in which they were concentrated by evapora- 

 tion. These earlier dolomites are continuous over wide areas, 

 with an almost uniform chemical composition. 



Maryland Geological Survey. 



Under the vigorous direction of the State Geologist, Prof. W. 

 Bullock Clark, the Maryland Geological Survey has just issued 

 its third volume ; one of a series which in type and illustration 

 is one of the most excellent of all the geological reports pub- 

 lished in the United States. The present volume deals wholly 

 with questions of economic geology treated from a scientific as 

 well as a practical point of view. It is, in fact, a manual on road- 

 materials and road-construction. The dependence of the highways 

 upon the surface configuration of the land, and the bearing of 

 the distribution of temperature and rainfall are pointed out. 

 Attention is rightly paid to the relationship between the stony 

 structure of the ground and the roads. The questions of con- 

 struction and repair, and the qualities of road-metals are dealt 

 with in detail, and the construction of sample roads is described. 

 Various administrative matters are also dealt with. Illustrations 

 are given of the method of road-making since early times ; there 

 are numerous photographic illustrations of types of roads formed 

 of different materials, including types of bad roads in Maryland ; 

 and there are photo-micrographs of rock-sections of road- 

 material. 



Geology of Indiana. 



A bulky volume of 1741 octavo pages forms the "Twenty-third 

 Annual Report of the Department of Geology and Natural 

 Resources for the State of Indiana," under the direction of Mr. 

 W. S. Blatchley, State Geologist. It comprises the result of a 

 careful survey of the coal area of Indiana, giving full details of 

 the physical features and stratigraphy, of the mines and method 



NO. 1590, VOL. 61] 



of mining, with analyses of the coal. The work is profusely 

 illustrated with maps and sections, and not the least interesting 

 are the sections of faults and disturbances and evidences of irregu- 

 larities in the coal-seams due to local thickening by disturbance, 

 or to original deposition, or to erosion in Carboniferous or later 

 periods. A report is made on the natural gas which occurs in 

 the Trenton limestone, and is sealed up beneath the Utica shale. 

 The first boring was made in 1884, and the gas was tapped at a 

 depth of about 1 100 feet. The Trenton limestone was proved 

 to be both the source and the reservoir of the gas. 

 Geological Survey of Canada. 

 The " Annual Report of the Geological Survey of Canada for 

 the year 1897 (1899)" has just reached us. It is a composite 

 volume, containing six individual reports separately paged, but 

 all indexed together with special references to each. As the 

 progress of the survey has been noticed already in Nature, 

 when dealing with the Annual Summary Reports of the director. 

 Dr. G. M. Dawson, it will suffice to call attention to this im- 

 portant volume which contains detailed accounts of Archnean, 

 Palaeozoic and Pleistocene deposits, with full descriptions of 

 the economic products. There is a special report on the mineral 

 resources of New Brunswick, by Mr. L. W. Bailey, and another 

 on mineral statistics and mines, by Mr. E. D. Ingall. The 

 volume is illustrated by a number of maps and plates. One of 

 the most effective views is that of the Devil's Rapids on Chandiere 

 river, Quebec. It illustrates a report on the surface geology 

 and auriferous deposits of South-eastern Quebec, by Mr. R. 

 Chalmers. 



ELECTRO-CUL TURE. 

 HTHE results obtained by culture under the influence of electric 

 -*- light are fairly well known, and the growing of lettuce for 

 salads, in spacious greenhouses with the aid of electric light, is 

 already a profitable industrial pursuit in the United States (near 

 Chicago and elsewhere). However, the use of electric currents 

 for stimulating vegetation, although it was studied more than fifty 

 years ago (by Ross, in 1844-46 ; continued by Forster, Sheppard, 

 Fichtner, &c.), still remains unsettled. A communication upon 

 this subject, made by a Russian engineer, V. A. Tyurin, before the 

 St. Petersburg Electro-Technical Society, contains some welcome 

 information upon the work done in this direction in Russia by 

 M. Spyeshneff and M. Kravkoff. The former experimented a 

 few years ago on three different lines. Repeating well-known 

 experiments on electrified seeds, he ascertained once more that 

 such seeds germinated more rapidly, a nd gave better fruit and 

 better crops (from two and a half to six times higher), than seeds 

 that had not been submitted to preliminary electrification. 

 Repeating next the experiments of Ross— that is, burying in the 

 soil one copper and one zinc plate, placed vertically and con- 

 nected by a wire, he found that potatoes and roots grown in the 

 electrified space gave crops three times heavier than those which 

 were grown close by on a test plot ; the carrots attained a quite 

 unusual size, of from ten to twelve inches in diameter. Spyesh- 

 nefPs third series of experiments was more original. He planted 

 on his experimental plot, about ten yards apart, wooden posts 

 provided at their tops with metallic aigrettes connected 

 together by wires, so as to cultivate his plants under a sort 

 of network of wires. He obtained some striking results, 

 one of which was that the growth and the ripening of barley 

 were accelerated by twelve days. Quite recently M. Kravkoff 

 undertook a series of laboratory experiments upon boxes of soil 

 submitted to electric currents. The temperature of the soil was 

 raised by these currents ; its moisture decreased first, but began 

 to increase after a course of three weeks (the same increase of 

 moisture was also noticed by Fichtner) ; and finally, the amount of 

 vegetable matter iij the soil was increased by the electric currents. 

 With what is now known upon the influence of micro-organisms 

 upon vegetation, further research on similar lines is most desir- 

 able and very promising. 



SCIENTIFIC SERIALS. 



"Y-RY. Journal of the Royal Microscopical Society for April con- 

 tains the President's Annual Address, the last instalment of his 

 valuable series of addresses on the mathematics of the construc- 

 tion of microscopic lenses. In this address, Mr. E. M. Nelson 

 devotes himself to the aplanatic immersion front and the 

 Huyghenian eye-piece, and deals with the errors of this lens, 

 viz. chromatism, curvature of image, distortion, and astigmatism. 



