part 2] geology or the wabble delta. 129 



fracture as well, though to a less and more variable extent, 

 proving that the disruption of this little tongue took place while 

 the magma was yet but partly consolidated. 



In another instructive instance exposed by the tramway-cutting 

 several elongated patches of granite lie in the marble severed from 

 the main vertically intruded vein, two of them measuring each over 

 a foot in length, bluntly pointed at both ends, and, like the parent 

 dyke, completely bordered by pyroxene and phlogopite shells. 



A fluid, or at least a plastic, condition for these portions of the 

 intrusion, during and immediately after its dismemberment, is 

 indicated by the continuity of the reaction-shells, as well as by the 

 foliated character of the igneous matter, the planes running more 

 or less parallel to the longer axes of the lumps, and also to the 

 length of the dyke : that is, vertically. The marble immediately 

 around the lumps is devoid of distinct bedding-planes, but these 

 are visible a short distance away dipping at a moderate angle from 

 left to right. 



Were it not for their relative position, ill-defined boundaries, and 

 reaction-zones, the smaller granite-patches in the marble would 

 certainly be interpreted as boulders. 



Other tine examples of disrupted veins exhibiting similar 

 peculiarities were found in the calcite strip on the Umzimkulu 

 River, and the united testimony afforded by all these occurrences 

 rules out all possibility of a xenolithic nature for such bodies. 



A section (34.09) from the margin of a vein 6 cm. wide in the 

 c.ilcite strip on F.O. shows abundant fresh scapolite — from its 

 interference colours probably wernerite — and a greenish diopside, 

 bordered by or intergrown with a little dark-green hornblende. 



It is important to note that, whenever scapolite occurs, it is 

 developed at the actual contact between the granite and the altered 

 dolomite, just as has been so well recorded by J. F. Kemp & A. 

 Hollick 1 at Warwick (N.Y.). Though the Natal occurrences are 

 only on a very small scale, the opinion was formed that the rock 

 belonged to the marbles ; but Kemp & Hollick, dealing with bands 

 several feet at least in breadth, have regarded it as a modification 

 of the granite. A more suitable way out of the difficulty would 

 perhaps be to consider the diopside-scapolite rocks as constituting 

 a hybrid type, for they have arisen through the combination of 

 matter contributed both by the intrusion and the dolomitic lime- 

 stones invaded. 



V. The Chondbodite- Marbles. 



These are interesting, partly because of the nature of the 

 dominant mineral, and partly because of their behaviour with 

 reference to the igneous contacts with which they are associated. 



In the strip of 'calcite' on F.O. along the right bank of the 

 Umzimkulu there are streaks of marble characterized by orange- 

 yellow or brownish chondrodite, and these are invariably separated 



1 Aim. N.Y. Acad. Sci. vol. vii (1894) pp. G44 et seqq. 



