Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/156

 than the Tulbagh coal, which is an equivalent of our Coal-measures.

The " Karoo formation " also occurs in a small belt on the sea- coast of Natal, which belt is never broader than from seven to eight miles, if so much. Beds of the Karoo series are well exposed at the Umgeni mouth and also at the Ifumi river. Any one who has been to Pietermaritzburg must have observed cuttings on the road, about seven or eight miles before he reaches the capital, in a dark shaly rock, with large boulders of older rocks imbedded, of granite, gneiss, slate, and also frequently of greenstone (fig. 2). These boulders are so characteristic of African scenery that they have received general attention. The boulders, often of very large size, are imbedded in a soft grit and shaly clay, containing small particles of mica.

Fig. 2. — Irregular boulders of Greenstone, sometimes Granite or Gneiss, imbedded in clay and grit.

The boulders seem to have been formed on the spot, or at least have not travelled very far, as many of them have kept their angular shape, and they seem to have undergone rather a process of decomposition than of rolling. These beds (" boulder-beds ") extend often over a very large area, and pass everywhere beneath the dark shale, which represents the base of the Karoo plant-beds. This is proved by a section at Thornville, and also on the sea-coast of Natal at several places, amongst them at the Umgeni valley and the Ifumi river. At the Umgeni and Durban the sections are as in figs. 3 & 4. Both these sections show that the plant-bearing shales and sandstones rest unconformably on the older Table-Mountain Sandstone, and also that the boulder-bed lies at the base of these plant- beds.

The same is shown at part of the road between Pietermaritzburg and Thornville (see Section, Pl. II.).

The boulder-bed here, in the same way as in the other sections, passes gradually into the shale of Pietermaritzburg, which, as I think, belongs to the lowest bed of the Karoo series. We learn from the Geological Survey of India that almost the same formation of