On differences in chemical composition between the central and marginal zones of granite veins : with further evidence of exchanges between such veins and the contact rocks / by William Mackie.

  • Mackie, William.
Date:
[1900]
Catalogue details

Licence: In copyright

Credit: On differences in chemical composition between the central and marginal zones of granite veins : with further evidence of exchanges between such veins and the contact rocks / by William Mackie. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    7/27 (page 99)
    Relation of composition of veins to that of contact rocks. decided evidence of other and no less interesting differences which also appear to arise from the operation of the same or similar causes. I refer to the differences which, as shown by Evidence of analyses, obtain between the composition internal differen- of the Central and marginal zones of the tiation in veins. granite veins, and which in the case of at least one substance may without exaggeration be fitly described as extreme. Such differences point to the fact of a remarkable Correlation of degree of differentiation having taken place differentiation with ill the veins tliemselves, and in conjunction exchange. with the analyses of the contact rocks they show that with this internal differentiation must be correlated such exchanges as have talien place. Some little evidence has also been obtained in favour of the view that such granite veins owe their composition in part at least to the Character of the rocks into which they have been intruded. This to some extent is a necessary corollary to the theory of exchange. There is also evidence to show that possible differ- Some results due cnces in the temperatures of the intruded and to temperature contact I’ocks have had something to do with differences. certain of the results observed. For convenience of reference, the analyses are divided into two main series—the (A) series, or those of the Eothes Burn Arrangement of granite veiiis, with their associated contact analyses. rocks; and the (i?) series, or those of the Portsoy shore, with their associated rocks. The (A) series are tabulated in four groups— 1st. A group of five analyses from the central parts of each of the granite veins. 2nd. A group of five analyses from the margins of the corres- ponding veins. 3rd. A group of four analyses from proximal positions in the 'Contact schists in the case of four out of the five of these veins. 4th. A gi’oup of four analyses from a distal position in the 'Contact rocks in the case of the four corresponding veins. A similar grouping of central and marginal analyses of the granite veins, and of proximal and distal in the case of the contact rocks, has been made as regards Series (A). The correlated analyses in the several groups are indicated by corresponding letters, ah c d e. The composition of the centre of a vein can thus be compared with its com- position at the margin; while the composition of the enclosing rocks at a point in proximity to the granite vein can be com- pared with its composition at a distance from the vein, as well ' as with the composition at the margin or at centre of the Series (A). Series (B),