THE GEOLOGY OF THE NEIGHBOURHOOD 

 OF STELLENBOSCH. 



By Professor S. J. Shand. 

 {Plates 4-5 and six text figures.) 



The geology of the Stellenbosch district was discussed very 

 briefly in the First Annual Report of the Geological Commission, 

 published in 1896, and it is depicted on a small scale in Sheet T 

 of the geological map of the Cape of Good Hope. The present 

 occasion seems appropriate for the presentation of the subject 

 hi somewhat greater detail, in order that the account may serve 

 as a guide to students of the University of Stellenbosch. The 

 writer has naturally paid much attention to local geology during 

 his six years of residence in Stellenbosch, and has mapped part 

 of the district on a large scale. There are certain points whose 

 inter()retation is not yet clear, and which can only be elucidated 

 by further mapping carried beyond the tract of country which 

 we may fairly call " the neighbourhood of Stellenbosch." Never- 

 theless, it should be possible, and it will perhaps be useful, to 

 submit a fuller account of the geology of our neighbourhood 

 than has yet appeared, laying stress on what is known and indi- 

 cating what is still obscure. 



Five geological formations lie under our feet or heaped u]) 

 in the mountains which surround us. One of these consists of 

 tiie steeply tilted slates and sandstones, to which the name of 

 the Mahnesbnry Series has been given ; these are, perhaps, the 

 oldest rocks exposed in the district. Less well known, because 

 less well exposed, are the greatly disturbed conglomerates and 

 sand.stones, which emerge with a north-westerly strike from the 

 mouth of Jonker's Hoek, and contiime across Ida's Valley to- 

 wards Elsenburg. To these rocks Rogers gave the provisional 

 name of the Freneh Hoek Series; the determination of their 

 age and their relation to the Malmesbury beds is the foremost 

 geological problem which this district presents. The granite 

 masses which penetrate the Malmesbury Series constitute our 

 third formation. Younger than any of these, and found only 

 on the tops of the mountains, for the most part above the 1,000- 

 feet level, is the Table Mountain Sandstone; and youngest of all, 

 flooring the valley in which we reside, is the thick Alluvium of 

 Eerste River. 



The areas where these rocks are exposed, or throughout 

 which they may reasonably be inferred to extend, are indicated 

 on the accompanying map (Plate 5). An unfortunate circum- 

 stance, which introduces difficulties into what should otherwise 

 be a very simple piece of geological mapping, is that contacts 

 or junctions between the various formations are almost nowhere 

 exposed to view ; and consequently the boundary lines separating 



