VOLCANIC PIPES 357 



are.olivine, diopside, chrome-diopside, enstatite, brown 

 mica, garnet, ilmenite, magnetite, perofskite, and in 

 smaller quantities, hornblende, tremolite, cyanite, cor- 

 undum and the diamond. 1 The blue-ground includes 

 abundant fragments of rocks torn from the sides of the 

 pipes during their formation, and varying in size from 

 microscopic fragments to masses hundreds of feet 

 across. These larger inclusions are commonly rounded, 

 sometimes to such a degree as to have given rise to 

 the erroneous impression that they had been derived 

 from water-formed conglomerates. 



In addition to the inclusions derived from the country 

 rocks exposed in the workings there are boulders of 

 intermediate, basic, and ultrabasic rocks, which have 

 doubtless been brought up from considerable depths, 

 as well as fragments which have fallen down into the 

 pipes from strata which were at one time penetrated by 

 the latter, but which have long since been removed by 

 denudation from over the area in which the pipes occur. 

 For example, at the Wesselton Mine the highest strata 

 surrounding the pipe are shales belonging to the Dwyka 

 series ; but in the blue-ground there have been found 2 a 

 lenticular mass of coal and two blocks of sandstone, one 

 showing the remains of the fish Acrolepis and the other 

 those of a reptile Chelyoposaurus allied to Procolophon* 

 This shows that the pipe must have penetrated the 



1 Carvill Lewis, loc. cit. ; H. Harger, T. G. S. S. A., vol. viii., p. 127, 

 1905. 



2 These statements have been denied by Voit in Monatsbericliten d. 

 deutsch. geol. Gesellsclutft, 1908, p. 102 ; but have been verified by one of 

 us in conversation with Mr. Jones, the finder of the inclusions. 



:! E. Broom, Rec. Albany Museum, vol. i., p. 184, 1904. 



