The Sutherland Volcanic Pipes. 77 



land breccias, have been found in them," nor have the fragments 

 of eclogite. 



Comparison with the Kimberley and Other Pipes North of 



the Orange Eiver. 



The constituents of the Kimberley group of pipes are fairly well 

 known, thanks to the many mineralogists who have examined the 

 materials brought to light by the progress of mining operations, but 

 less information is available concerning the Jagers Fontein, Monas- 

 tery, Pretoria, and other mines outside the Kimberley area.f 



The more important constituents of the Kimberley blue-ground 

 are the following : Olivine and its alteration product serpentine, 

 enstatite (bronzite), chrome diopside, smaragdite, biotite, garnet, 

 perofskite, magnetite, chromite, picotite, ilmenite ; the less abun- 

 dant minerals are apatite, epidote, orthite, tremolite, tourmaline, 

 rutile, sphene, leucoxene, and diamond.]: The rhombic pyroxene, 

 enstatite or bronzite, which is usually considered to be an important 

 constituent, seems to have been much more abundant in the earlier 

 worked blue-ground than in the later worked rock obtained from 

 greater depths. § An examination of some specimens in the South 

 African Museum from the lower levels in de Beer's Mine reveals a 

 very small amount of this mineral. Enstatite is an abundant 

 mineral in an enstatite-garnet-augite-hornblende rock from the 

 Monastery Mine (0. E. C.) preserved in the Museum. As a result of 

 his examination of the blue-ground or Kimberley, Professor Carvill 

 Lewis came to the conclusion that it was related to melilite-basalt, 

 though owing, as he suspected, to the alteration his specimens had 

 undergone, the melilite could not be identified. || The intimate 

 association of melilite-basalt with breccias which have a distinct 

 similarity to the blue-ground, though differing from it in the greater 

 abundance of debris derived from sedimentary rocks and, in the case 

 of the Matjes Fontein pipe, from deep-seated acid igneous rocks, is 

 certainly very suggestive, and warrants the expectation that melilite 

 rocks will one day be found with the typical blue-ground at Kim- 

 berley. As we have stated on a previous page, the melilite-basalt 

 has not been met with at Silver Dam, nor is the breccia in the 



* See Schwarz, op. cit., p. 54. 



f The most useful publications dealing with the constituents of the Kimberley 

 group are : N. S. Maskelyne and Flight, Q. J. G. S., xxx., 1874, pp. 408-416 ; L. de 

 Launay, "Les diamants du Cap," Paris, 1897; H. C. Lewis, " Genesis and Matrix 

 of the Diamond," London, 1897, edited by Professor Bonney, 



I Taken from Lewis, op. cit., Sect. II. 



§ See Bonney, Geol. Mag., 1895, p. 496, 



jj Lewis, op. cit., p. 49. 



