2l<i Geological Society. 



of a similar agency, in opposition to the opinions of other observers, 

 who had referred the formation of some to the decomposing action 

 of the atmosphere on granite (aided in some instances by human 

 agency), of others to the effect of glaciers, &c. 



2. " On the Copper-mines of Namaqualand." By R. N. Rubidge, 

 Esq., M.B. In a letter to Sir R. I. Murchison, F.G.S. 



On his examination of Namaqualand, in 1854, Dr. Rubidge found 

 that the conditions under which the metalliferous rocks occur there 

 differed from any which he had previously known, 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 at least the more 

 southern part of this mining district, present externally an iron- 

 stained surface, the rock being different from the gneiss on either 

 side, and that the general south dip of the rocks changes in the centre 

 of the run to the opposite direction, and then recovers the former 

 direction for a variable distance from half a mile to twelve miles, 

 when similar changes of dip occur, with or without metalliferous 

 indications. These linear alterations of dip, or axes, present two 

 chief varieties, termed by the author, respectively, " axes of change," 

 and " axes of disturbance." Some of the axes appear to be branched. 

 The surface of th'e metaUiferous runs is much cross-fissured and 

 decomposed; the rocks are stained of a bright green colour by 

 silicate of copper, and lumps of oxide of copper are scattered on the 

 surface, or in the fissures. When these are followed downwards, 

 they often widen at first into largish veins, which at depths varying 

 from 4 to 25 feet generally contract, sometimes terminating abruptly. 

 At a greater depth purple sulphuret of copper occurs, and still lower 

 copper-pyrites, either in fissures between masses of slightly decom- 

 posed granite, or diffused in grains throughout the granite. Dr. 

 Rubidge described the relations of the Springbok, Koperberg, Con- 

 cordia, Hoeklip, Rietburg, and other mines, to the several metallife- 

 rous axes, as far as his opportunities had enabled him to form an 

 opinion ; and then offered some remarks on the probable origin of 

 the succession of the ores observed in the axes, several of the facts 

 connected with them pointing, in his opinion, to the agency of water, 

 and perhaps of magneto- electrical force as having produced many of 

 the phaenomena. The mines to the northward, near Henkries and 

 Pella, present different conditions of the metalliferous rocks to those 

 of Springbok and the southern mines. In the Orange River county, 

 homblendic, micaceous, and other schistose rocks are penetrated by 

 granitic dykes and masses ; and the copper-ores occur in small 

 masses, disseminated through the crystalline veins, and sometimes 

 in the rocks themselves. 



