NATURE 



405 



THURSDAY, MARCH 5, 1885 



ORE DEPOSITS 

 A Treatise on Ore Deposits. By J. Arthur Phillips, 

 F.R.S.. &c. Demy Svo, pp. 624 and Index ; 95 Wood- 

 cuts and I Plate. (London : Macmillan and Co., 1S84.) 

 A WORK in the English language upon ore deposits 

 has long been wanted, and geologists and mining 

 engineers may be congratulated that one so well qualified 

 to do justice to the subject as Mr. Phillips, undertook the 

 laborious task of writing a general treatise. 



Mr. Phillips divides his book into two parts ; Part I., 

 occupying one-sixth of the volume, treats of ore deposits 

 in general, and Part II. is devoted to a description of the 

 principal metal-mining regions of the world. 



We are glad to see that he admits a wide definition of 

 the term " ore : " " Although perhaps not strictly correct, 

 any material obtained by mining that contains a work- 

 able proportion of a metal is often called an ore, even if 

 the whole of the metal be present in the native state.'' 

 This is a common-sense and practical way of dealing with 

 the question. 



The classification of ore deposits is in the main the 

 same as that adopted by Whitney, in his " Metallic Wealth 

 of the United States," thirty years ago. Mr. Phillips 

 divides metalliferous deposits into the following groups : — 



I. Superficial 



a. Deposits formed by the mechanical action of water. 



b. Deposits resulting from chemical action. 



II. Stratified 



a. Deposits constituting the bulk of metalliferous beds 



formed by precipitation from aqueous solutions. 



b. Beds originally deposited from solution, but subse- 



quently altered by metamorphism. 



c. Ores disseminated through sedimentary beds, in which 



they have been chemically deposited. 



III. UNSTRATIFIED 



a. True veins. 



b. Segregated veins. 



c. Gash veins. 



d. Impregnations. 



e. Stockworks. 



f. Fahlbands. 



g. Contact deposits. 



//. Chambers or pockets. 



This classification is the only blemish of any importance 

 in the volume, and we greatly regret that the author did 

 not cast off the trammels of tradition and strike out a new 

 line for himself. 



In the first place, we are disposed to quarrel with the 

 separation of superficial deposits, as described by Mr. 

 Phillips, from stratified deposits ; we do not see how they 

 can be logically separated. Speaking of the old auriferous 

 gravels of the Sierra Nevada of California, the author's 

 words are: — "These, which are sometimes known as 

 blue gravels, were formerly believed to be of marine 

 origin, but are now recognised as materials brought down 

 by the agency of currents of fresh water from the moun- 

 tains high above them and deposited, either in the beds 

 of ancient rivers, or in lake-like expansions of such 

 streams." Surely, therefore, they are stratified. Further- 

 more, the term " superficial " should have been avoided 

 as misleading, because the student will naturally infer 

 that the chief characteristic of such deposits is that they 

 occur at the surface ; but when we find gold- and tin- 

 Vol. XXXI.— No. 801 



bearing gravels buried at a depth of more than 100 feet 

 under other strata and lava-flows of Pliocene or Miocene 

 age, and worked as true mines, the word " superficial " 

 seems singularly inappropriate. The author admits that 

 the term " might at first sight appear a misnomer," but 

 defends it on the ground that "a volcanic capping is by 

 no means universal, and the uncovered beds of this age 

 are of the greatest importance to the miner." When 

 Whitney's book was written the name was more in 

 harmony with the facts, as the deep leads had not been 

 discovered : but even then there was nothing to justify 

 the separation of the old alluvia from the class of stratified 

 deposits. 



The three subdivisions of the stratified deposits are 

 useful for impressing upon the mind the most important 

 varieties of this class ; on the other hand, when we come 

 to the unstratified deposits we consider that the author 

 has been unwisely conservative. 



Why should the geologist step in and call certain 

 mineral veins " true," and thereby cast a sort of stigma 

 upon others which do not fit in with his preconceived 

 theories ? Mr. Phillips, like most authors, uses the word 

 " true vein " as synonymous with " fissure vein " ; but as 

 it appears that many of the sheet-like mineral masses 

 called "lodes" or "reefs" by miners are not filled up 

 cracks, it seems a pity that the worship of the " fissure 

 vein " should be continued. 



A useful summary is given of the various hypotheses 

 which have been propounded concerning the genesis of 

 mineral veins, and due attention is paid to the discoveries 

 of Prof. Sandberger, which have an important bearing 

 upon the theory of lateral secretion. The author ulti- 

 mately concludes that both lateral secretion and the 

 ascension of mineral-bearing waters have contributed to 

 the filling up of fissures with the various minerals now 

 constituting the veins. 



Though he keeps up the old subdivision of " segregated 

 veins" as distinct from true veins, Mr. Phillips is justly 

 doubtful whether such a distinction can always be logi- 

 cally maintained. 



With reference to the " impregnations," it is probable 

 that some of the most important Cornish tin lodes in 

 granite may be classed under this head, and therefore 

 this subdivision might be made to include a good deal 

 more than the carbonas. 



The word " Stockwork " is unfortunately consecrated 

 by long usage, and it will not be easy to evict it from 

 mining literature ; but it is a pity that no English term has 

 been coined to denote this mode of occurrence. Speaking of 

 Polberrow mine, Mr. Phillips says it "appears to be the 

 only stockwork ever extensively worked in clay slate." 

 This is not the case. The three openworks in Cornwall 

 known as Minear Downs, Mulberry and Wheal Prosper 

 are other instances of stockworks in clay slate. They 

 produced 203 tons of dressed tin ore in 1883, and the 

 excavations are certainly sufficiently large to say that the 

 deposits have been " extensively worked." Henwood's 

 account of Wheal Music (Trans. Roy. Geol. Soc. Cornwall, 

 vol. v. p. 98) shows that it was a stockwork in clay slate, 

 worked for copper ore. 



It seems a mistake to retain the " fahlbands " among 

 the unstratified deposits. They are pyritiferous beds 

 among metamorphic rocks. At Kongsberg they consti- 



