F. Chapman— The Olifant Klip from Natal, etc. 553 



up an(3 rippled, whilst between the folds, which are often sharp 

 and V-shaped, the calcareous and other minerals lie in fibrous 

 bands or intermingled with quartz-grains. 



On the margins of the sandstone fragments some dolomite rhombs 

 may be detected. 



This ' Olifant Rock' is not a true dolomite, but a crushed limestone 

 with much siliceous interstitial matter, and the crushing has given 

 rise to a pretty 'rippling' of the granular portion, such as one 

 often sees in the Skiddaw Slates and other rocks of a similar nature. 



II. — The large block, from near the Hospital, is broken on one 

 side, and has been sawn across carefully on the other to show its 

 structure ; and a large portion of the original surface exposed by 

 weathering is seen on the rest of the specimen. It is evidently 

 a portion of a sub-lenticular mass, consisting of an inner calcareo- 

 siliceous material and an outer finer-grained siliceous and limonitic 

 crust. 



The whole block is strongly suggestive of its having been 

 a lenticular mass, produced by intense folding, which has resulted 

 in two contiguous, but differently constituted, layers being cut ofif 

 in their continuity from the rest of the mass, as may be seen in 

 certain of the folded Palaeozoic rocks of the West of England, where 

 a series of sigmoidal folds ultimately give rise to a band of separate 

 lenticles. (See for instance Dr. H. Hicks' paper on " Folds and 

 Faults in the North Devon Eocks," Geol. Mag., 1893, pp. 3-9, 

 especially the woodcut at p. 5.) 



Fig. 3. — Sigmoidal folding in Devonian Rocks,- east side of Hele Bay, Ilfracombe. 

 To illustrate the origin of the concentric Olifant Klip blocks. 



A. Ordinary sigmoidal fold in limestone. 



B. Dumb-bell shaped fold due to pressure and thrust. 



C. Isolated fold with crust and core. 



D. Crushed and contorted slaty beds. 



From a photograph by F. Chapman, 1899. 



In explanation of the formation of the travelled and broken 

 blocks found in the Ecca Shale near Ladysraith, as lenticles, in 

 contorted Palaeozoic strata, which have subsequently been broken out 

 and then shifted by water or ice-action, the above section is given. 



