No CrossRef data available.
The genetic classification of rocks and ore deposits
Published online by Cambridge University Press: 14 March 2018
Extract
During the last decade there has been no lack of controversy on the subject of rock classification, but the dispute has concerned igneous rocks almost entirely. Petrography has been threatened by an effort to reduce it to an independent science of igneous rocks, and in consequence of this there has been a tendency to neglect its wider aspects. Important as igneous rocks are, their formation is less well understood than is that of some other sub-groups of rocks ; moreover, they constitute one only of some six or seven sub-groups, and it is the business of petrography as a science to deal with these rocks as a whole. The student of petrography should be encouraged to take this wider view. He shonld look at these different sub-groups of rocks in their proper geological perspective, and approach the study of the classification of igneous rocks with a knowledge of the principles that are applicable to the classification of rocks as a whole.
The discussion concerning the classification of ore deposits has proceeded on independent lines, and in a more well-balanced manner than has that of rocks. With ore deposits, as with rocks generally, genetic principles have triumphed; but the application of these principles to rocks long preceded their application to ore deposits. Iu recent years it has become apparent that the fundamental requirements for the classification of rocks and ore deposits are essentially the same ; and in view of the identity of their interests, both subjects are treated in this paper.
The aims of this paper are : To define the basis of genetic classification ; to give a brief historical account of classification on genetic-geological principles ; to point out defects in the present system of arrangement ; and to suggest an altemmtive scheme of grouping that is in closer accord with geological and genetic principles.
- Type
- Research Article
- Information
- Mineralogical magazine and journal of the Mineralogical Society , Volume 17 , Issue 79 , July 1914 , pp. 55 - 85
- Copyright
- Copyright © The Mineralogical Society of Great Britain and Ireland 1914
References
page 59 note 1 David Forbes was one of the pioneers of microscopical petrography. As early as 1852 he had begun his rook studies with the microscope, working at slices which were cut'for him by Osehatz of Berlin, who appears to have entered this field of activity independently of Sorby. This was some ten years prior to the date when Sorby, sitting with Zirkel on the Draehenfels, explained to him the advantage of examining rock slices microscopically, and described to him how slices were prepared. It is not unfair to the memory of Sorby to say that, though he was perhaps without equal as a master of the technique of rockslicing, he was no match for Forbes as a petrographer. It is indeed doubtful if, during tile late fifties and early sixties, there was anywhere a worker who had made such a wide study of this subject as Forbes. tie was a practised observer in this line of work, thanks almost entirely to his own foresight and enthusiasm, before Zirkel had realized its value. He did not limit his microscopical investigation to slices ; for he tells us that ‘thin splinters of rocks and powdered fragments, mounted in Canada balsam, may also .be examined with advantage’. His paper on ‘The Microscope in Geology’ was indeed a valuable early scientific contribution to microscopical petrography, excellently illustrated with coloured and other drawings of rook slices, and embodying work done at a time when there was no literature on the subject bearing on the broad outlook which he entertained.
page 61 note 1 Renevier, E., ‘A petrographical (sic) classification of rocks,’ Proc. Geol. Assoc., 1880, vol. vi, p. 426 Google Scholar. fuller, Fern account see 'Classification pétrogénique,' Bull. Soc. Vaud., 1882, vol. xviii, p. 93 Google Scholar.
page 79 note 1 According to Posepny, von Groddeck entertained the idea of a composite classification in which ' he hoped to represent one standpoini; by abscissae and the other by ordinates, so that the intersection would determine the type of deposit' (op. cit., infra, p. 2el). This idea has been applied by F. H. Hatch in a semi-genetic scheme recently proposed by him (Presid. Address, Inst. Mining and Metall, London, March 1914).