52 



THE GEOLOGIST. 



have attempted to establish this is somewhat defective, but I have 

 shown clearly that that on which it is denied is valueless. 



I have already described the interpolation of masses of granite 

 among the slate of Cape Town without displacement : this phenomenon 

 obtains to a much greater extent in Namaqualand ; great masses of 

 granite, with little if any evidence of stratification, pass gradually into 

 gneiss on either side, and, in fact, all round, without change of dip. 

 These are called locally "bosses," and their scaling off is remarkable, 

 giving them the rounded outline, whence their name. The same 

 thing is seen in the change of hornblende-schist into greenstone or 

 syenite, with large crystals of hornblende, ]N'umierou3 instances of 

 this occur ; one of the most striking is between Klein Pella and 

 Oomsdrift.* 



I have mentioned in a former Paper that the twists of the strata 

 in which the copper-ore is deposited occur in gneiss, and when a sec- 

 tion is seen on a hill- side no granite is visible, but when worked to 

 any considerable depth, the rock loses its laminated character and be- 

 comes a felspathic granite or greenstone. A remarkable section was 

 observed near Pella : a stream had worked a deep channel in the 

 rocks ; the edges of the ravine so formed were of well-marked gneiss, 

 while the water ran over a bed of granite without trace of lamina- 

 tion, the gneiss preserving the same dip on either side of the ravine. 

 Indeed, it appeared to me as if metamorphosis of the rock into felspa- 

 thic granite was the normal state below, while the gneissic lamina- 

 tion was a superficial indication of the old stratification-planes. 

 While on this subject I will mention what appears to me to be a 

 singular character of our palseozoic rocks here. The specimens I 

 have sent home will show that all the Devonian fossils here lose 

 every trace of their carbonate of lime. They are preserved, often 

 very perfectly, in oxide of iron, but in my experience they are seen 

 only on the exposed edges of the rocks, be these greatly inclined, as 

 at Chatty and llermansdorp, or onl)^ slightly so, as at Coxcomb and 

 Jeffrey's bay. At Chatty I have seen a mass hollowed out in all 

 directions by the decay of the encrinites on the edges, while tracing 

 the same layer deeper in, it lost all trace of fossils. Frequent repeti- 

 tious of this seemed to me to establish it as a rule that the fossils in 

 the rock were only exposed by decomposition. Still it may be merely 

 accidental. I should be glad to learn whetlier it is so or not. 



I liave stated that in the metallic twists, or saddles, I never saw 

 granite in what I could consider the position of an intrusive rock. In 

 one of the accessory twists which meet the metallic saddles at various 

 angles, and which in section on a flat surface have the appearance of 

 a feather, the sliaft (a h) of the feather was 

 composed of micaceous schist, with a few rather 

 large crystals of felspar. I have freqiunitly seen 

 irregular-shaped patches of mica-schist follow- 

 ing neitlier strike, nor any law that I could per- 

 ceive, among tlie gneiss. Granite occurred in 

 the same way in other spots. 



* Diil'l-ford (of Iho Orange river). 



