348 THE SUTHERLAND PIPES 



which still adheres to the serpentine pseudomorphs ; 

 augite and magnetite are the other constituents that 

 have been recognised, and they are in very minute 

 grains and crystals. The steam-holes in this lava are 

 filled with calcite, analcite, natrolite, and other zeolites, 

 but silica, which in the form of quartz or chalcedony 

 is frequently found in the steam-holes of the ancient 

 Zeekoe Baard lavas and those of the Stormberg series, 

 has not been found in the Sutherland Commonage 

 amygdaloid s. 



At Matjes Fontein, a farm nine miles south-east of 

 Sutherland, there is a pipe partially filled with melilite- 

 basalt of rather peculiar characters l and partly with a 

 gritty breccia containing large fragments of granite, 

 dolerite of the Karroo type, quartzite and other sedi- 

 mentary rocks, mica, ilmenite and hornblende. The 

 three latter constituents are identical in nature with 

 the same minerals in the Silver Dam pipe to be men- 

 tioned presently. The melilite-basalt of this outcrop is 

 composed of olivine, melilite, perofskite, biotite, mag- 

 netite, calcite and serpentinous fibres, probably derived 

 from a glassy ground mass. Excepting the presence of 

 calcite and the serpentine fibres the rock is remarkably 

 fresh, and differs in several respects from the other 

 melilite-basalts. It shows a marked flow-structure. 



In the remaining pipes there is no large body of ig- 

 neous rock corresponding to the melilite-basalts and the 

 glassy lava described above. 



At Silver Dam, a part of the farm Matjes Fontein in 

 Sutherland, there is a breccia-filled pipe about 180 feet 

 1 See G. O., viii., and T. P. S. S. A., vol. xv., 1904, p. 61. 



