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THE SUTHEBLAND VOLCANIC PIPES AND THEIE 

 EELATIONSHIP TO OTHEE VENTS IN SOUTH AFBICA. 



By A. W. Eogeks and A. L. du Toit. 



(Bead March 2, 1904.) 



During the recent geological survey of Sutherland a considerable- 

 number of volcanic pipes were met with. They are all of a peculiar 

 type, and are more nearly allied to the Kimberley pipes than to 

 the more usual kind of volcanic vents that are represented in this 

 country by the Stormberg necks. 



In this paper we propose to describe these volcanoes, and to 

 point out their relationship to similar vents in other parts of 

 South Africa, and their more or less close resemblance to some 

 foreign vents. 



In the Sutherland Division the necks occur on the village 

 commonage ; on the farm Matjes Fontein, about nine miles south- 

 east of the village of Sutherland ; in the immediate neighbourhood 

 of Saltpetre Kop, a short distance to the north-east of Matjes Fon- 

 tein ; on Blaauw Blommetjes Keep, 2|- miles north-west of the Kop ; 

 on De Vrede, to the south of Saltpetre Kop ; and on the banks of 

 Portugal's Eiver, east of De Vrede. There are probably several 

 others which escaped detection, but in the case of two shallow 

 depressions about two miles east of Sutherland village some of the 

 peculiar minerals characteristic of one class of the rocks occupying 

 the pipes were found in the surface soil. 



Many of the pipes are very inconspicuous, for their contents have 

 weathered away slightly faster than the surrounding rocks, and the 

 tendency to form a depression has been kept in check by the deposit 

 of silt and sand over the areas, so that there is nothing to distinguish 

 a depression due to the presence of a pipe from the shallow pans 

 that are frequently met with in the Upper Karroo. Other pipes are 

 fairly easily found owing to the weather-resisting qualities of some 

 of the rock in them ; and others again, such as the Saltpetre Kop 

 group, are very conspicuous from, that cause. 



All the vents in the Sutherland Division are surrounded by nearly 

 horizontal strata belonging to the lower part of the Beaufort series. 



