332 Reports and Proceedings—Geological Society of London. 
the special care of this Society, may continue to grow and flourish under the rule of 
Your Majesty as it has done under that of your illustrious predecessors. 
‘¢ That Your Majesty’s reign may be a long one and that it may overpass in lustre 
even those of the great Kings and Queens that have preceded you, is the earnest 
prayer of your devoted subjects.”’ 
The President then read the draft of a circular letter regarding the 
enhanced price of the Geological Survey Maps, which is to be sent 
to all institutions in the United Kingdom that are likely to be 
interested in the matter, bespeaking their support for a respectful 
representation to the Lords of H.M. Treasury. A draft of the terms 
in which this representation is to be made was also read. 
The following communications were read :— 
1. ‘* Dedolomitization in the Marble of Port Shepstone (Natal).’’ 
By F. H. Hatch, Ph.D., M.Inst.C.E., F.G.8., and R. H. Rastall, 
WiC eli Giese 
The Port Shepstone marble is shown by chemical analysis to be 
a dolomite (the molecular ratio of calcium carbonate to magnesium 
carbonate being as 3 : 2). It owes its marmorization to thermal 
metamorphism by an extensive intrusion of granite, which completely 
surrounds it and penetrates it in broad dykes. This instrusion took 
place at some time prior to the deposition of the Table Mountain or 
Waterberg Sandstone, and is therefore pre-Devonian. The dolomite 
is relegated to the Swaziland Period. 
The metamorphism of the dolomite under normal conditions is shown 
to have produced a saccharoidal marble of coarse texture, consisting 
almost entirely of carbonates; and the fact that neither periclase nor 
brucite has been produced in the normal marble is taken to indicate 
that the high-pressure conditions obtaining during the metamorphism 
precluded dedolomitization. In those places, however, where the 
dolomite contains blocks or boulders of earlier granitic rocks, inter- 
action took place between the magnesium and calcium carbonates of 
the dolomite and the silica and alumina provided by the inclusions, 
resulting in the production, in the zone of marble immediately 
surrounding the inclusions, of a number of interesting silicates of 
magnesium, calcium, and aluminium, such as olivine, forsterite, 
diopside, wollastonite, and phlogopite, as well as the oxides brucite 
and spinel. Magnesian compounds predominate, the excess of lime 
recrystallizing as calcite. A noteworthy feature is the absence 
of minerals such as garnet and cordierite, which are especially 
characteristic of low temperature metamorphism, thus indicating the 
prevalence of a high temperature during the metamorphism of the 
dolomite. 
The paper concludes with a reference to the occurrence of granite 
boulders as foreign inclusions in other limestones, and a discussion of 
the chemical reactions by which the formation of the above-mentioned 
minerals may be theoretically explained as a result of dedolomitization. 
Comparison is made with the dedolomitized Cambrian limestones of 
Assynt and Skye described by Dr. Teall and Mr. Harker, from which 
the Port Shepstone occurrence differs in the localization of the affected 
areas to reaction rims around foreign boulders, and in the part played 
by alumina in the formation of new minerals. 
