The Sutherland Volcanic Pipes. 1$ 



taining chrome-diopside, but it has not been found in the rock 

 fragments from Silver Dam, although it is abundant as isolated 

 and serpentinised crystals and fragments in the breccia. 



In some rounded fragments of eclogite from the Newlands mine 

 in Griqualand West, Professor Bonney * found garnet (pyrope), a 

 chrome-diopside of a much paler colour than the bright green augite 

 mentioned above from the Silver Dam and Monastery Mine rocks, 

 but apparently similar to the pale green augite of those rocks, and 

 small octahedral diamonds. He indicates the bearing of this dis- 

 covery on the origin of the diamond, which belongs primarily to the 

 noncrystalline ultrabasic rock and not to the blue-ground. The 

 evidence brought forward in his paper appears to be quite conclusive 

 on this point. 



The Newlands -Mine is on the Harts Eiver, north-west of Kim- 

 berley. The blue-ground fills an irregular pipe and fissures in slates 

 and other rocks belonging to the pre-Cape rocks of Griqualand 

 West,! but at the surface the pipe is surrounded by shales of the 

 Karroo formation as at Kimberley. The accounts of the serpentinous 

 breccia in dykes is interesting, and affords a parallel to the breccia 

 dykes of Saltpetre Kop and other localities in Sutherland. 



Comparison with the Pipes South of the Orange Eiver. 



In Mr. Dunn's paper, " On the Mode of Occurrence of Diamonds 

 in South Africa," J there is a short description of a pipe at Schiet 

 Fontein, Carnarvon, which is surrounded by shales turned up at the 

 contact with the breccia. No particulars of the contents of this 

 pipe or those near Hanover are known. At Balmoral (Eatel 

 Fontein) in the Fraserburg Division there is an admirably exposed 

 pipe.§ The surrounding rocks are sandstones and shales belonging 

 to the middle part (probably the Dicynodon beds) of the Beaufort 

 Series, and they dip away from the pipe. The pipe is about 300 feet 

 in diameter and nearly circular. The contents are more easily 

 weathered than the surrounding rock, so the pipe is marked by a 

 depression from 10 to 20 feet deep, with a vertical wall formed by 

 the Beaufort beds, except at one place where the surface water 

 drains off through a narrow gap in the sandstone wall. The 

 material filling the pipe is a soft blue clay containing fragments 

 of shale, sandstone, dolerite of the Karroo type, ilmenite, garnet, 



* Geol. Mag., 1899, pp. 309-321. , 



f See W. Graichen, "Die Newlands-diamantminen, Sud Africa," Zeitschrift 

 fur praktische Geologie, xi., 1903, pp. 448-452. 

 + Q. J. G. S., 1874, pp. 54-60. 

 § Sogers and Schwarz, Ann. Bep. Geol. Comm, for 1900, pp. 60-61, 



