1857.] RUBIDGE NAMAQUALAND. 233 



stone in it, it appears to me that it would have remained until it had 

 further widened and deepened the pot ; and in the process worn it- 

 self small, and been in its turn ejected. Such a process repeated, 

 even at long intervals, in geological periods, is sufficient to account 

 for the formation of "Rock-Basins," "Kettle and Pans," "Giant's 

 Pots," and similar phsenomena. 



The sea round our shores is now receding just as in Sweden, by 

 slow degrees, and has done so, at the same rate, in long past ages. 

 Although Dartmoor be now far from the sea, and the Kock-Basins 

 1417 feet above the sea-level, yet this surely is nothing against my 

 view of their origin, but tends only to give us an inkling of what is 

 meant by the "long periods" of geology. 



The contents of the Rock-Basin, lately discovered on Dartmoor, 

 are such as my views of their origin would have led me to expect, and 

 therefore I conclude it had never been disturbed since it was filled. 



[Note. — For notices of Rock-basins, &c., see Geol. Proceed, vol. iii. p. 704 ; 

 Quart. Journ. Geol. Soc. vol. x. p. 240; Neues Jahrb. 1854, p. 148; Gibbon's 

 Exploration of the Amazon, pp. 283, 291 ; Mactaggart's Canada, vol. i. p. 77. — 

 Edit.] 



2. On the Copper-mines of Namaqualand. B}^ Dr. R. N. 

 RuBiDGE. \In a Letter to Sir R. I. Murchison, F.G.SJ] 



[At the instance of a Mining Company, in 1854, Dr. Rubidge went 

 to Namaqualand to report upon its metal-producing capabilities. 



He found that the conditions under which the metalliferous rocks 

 occurred there differed from any which he had previously known or 

 read of, and that they did not take the character of " lodes," as 

 usually understood. On the contrary, he found that all the " runs 

 of ore" in the southern portion of the district visited had the fol- 

 lowing characters in common, as described in his letter.] 



Characters of the " runs'^ and of the metalliferous axes. — 1st. The 

 "runs of ore" presented externally a brown, iron-stained surface, 

 continuous to a greater or less distance; the rock being different 

 from the gneiss on either side of the " run," and has on the under 

 surface stains of silicate of copper (green) ; small masses of red 

 oxide also were often found on the surface. 



2ndly. On closer examination, I found that the dip of the rocks 

 changed in the centre of the "run" to the opposite direction, and 

 then resumed the same direction as the former. Thus at Springbok 

 Fontein the main dip of the country is south. It is changed to a 

 northerly dip on the " run," and the south dip is restored on the 

 northern side, and continues for half a mile, where it changes with- 

 out the occurrence of metalUferous deposits, This northern dip con- 

 tinues for perhaps twelve miles, and at Windhoek gives place to a 

 southerly dip, of about equal extent, which reaches to within about 

 four miles of Steinkopf, the Missionary Station ; these main changes 



s2 



