The Geology of the Marble Delta (Natal)

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Abstract
The crystalline dolomitic marbles near Port Shepstone have formed the subject of no less than three communications to this Society. That by C. L. Griesbach, written nearly half a century ago, gives us the first glimpses of this interesting occurrence; the next, by David Draper was fuller, but lacking in most of the important details; the third, by Dr. F. H. Hatch & Mr. R. H. Rastall is a particularly valuable contribution, especially from the petrographical standpoint: the intrusive relationship of the granite is placed beyond dispute, and the operation of the action known as dedolomitization is fully demonstrated. Consequently, it is not inappropriate that the principal conclusions arising out of the geological survey of the area (carried out in 1915–16) should be communicated through the same channel, especially as they confirm and amplify the expressions of Hatch & Rastall as to the nature of the metamorphic actions involved. The sole point of disagreement concerns the ‘boulder’ of alkali-granite, which, from the evidence available, can only have formed part of an intrusive tongue in the marble, while the other reputed instances of ‘inclusions’ must be placed in the same category. The object of the present paper is the description of this and certain other cases, where there has been an actual transfer of material from the intrusion across the contact to the rock invaded, a rather infrequent phenomenon, and one termed ‘contact-metasomatism’ by J. Barrell, and ‘pneumatolytic contact-metamorphism’ by Y. M. Groldschmidt; the action termed ‘calcitization’ is also described and

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