344 Albany Museum Records. 



Table Mountain series, and the process by which the bending is 

 accomplished, is that, when pressure comes ni)on a bed, the grains 

 of the sandstone adapt themselves by the parts under stress dis- 

 solving, and the material being redeposited where there is strain, 

 so that each grain accommodating itself without loosing its indi- 

 viduality, the whole stratum gradually assumes a new form with- 

 out showing any break in its continuity. 



Another striking instance is the replacement of pebbles in the 

 Johannesburg banket by calcite, as explained by Mr. Kuntz (6). 

 The quartz of the pebbles is entirely removed in the neighl)our- 

 hood of a spring carrying lime in solution, and its place taken by 

 calcite, so that there are pi^oduced limestone pebbles ; the imi)ossi- 

 bility of these latter being original is ])ointed out by the author. 



In the report on Prieska, Mr. Rogers and myself described a 

 peculiar dyke of quartz and felspar in the limestone series (7), a 

 portion of which was presented to the Albany Museum, and forms 

 specimen No. 9 of the rock collection. The dyke is for more than 

 half its bulk occupied by limestone, and I think this is probably 

 a case of an original pegmatite dyke in which a good deal of the 

 quartz has been subsequently eaten out and replaced by limestone. 



Replacement of silicates and quartz by pyrites is recorded by 

 Purington in the Rerezovsk district in Russia, near Ekateidnbourg, 

 (8) where a large area of granite has been converted into what 

 Karpinski has termed " berezite " (9), a rock consisting of musco- 

 vite, felspar and quartz, with a mixture of secondary pyrites 

 carrying gold. 



Suppose now that a boulder of quartzite, such as the Albany 

 Museum specimen, had lain for a very long time in a matrix 

 through which water containing iron pyrites in solution, or rather 

 capable of depositing iron pyrites, was continuously passing, it 

 is not speculating too freely to imagine that the quartzite boulder 

 would become in the end a nodule of iron ])yrites. In the Johan- 

 nesburg banket, a much older formation than the Molteno l)eds, 



(6) Transactions S.A. Geol. Soc, vol. VI, p. 74. 

 [1) Ann. Rept. Geol. Comm. for 1899, p. 78. 

 (8) Engineei'ing and Mining Joui-nal, June 13, 1903. 

 (9') Compte Reiulu, Congres Geol. International, 7 ieme session, 

 St. Petersburg, 1897, p. CCIX.i 



