22 Transactions of the South African Philosophical Society. 



erupted rocks of volcanic islands, though they are frequent in the 

 volcanic eruptions of continental areas."" Darwin's observation of 

 the serpentine on St. Paul's Eocks is taken to be a volcanic peridotite 

 though Professor Eenard states very strongly that the foliation of 

 the mass, and the drawing out of the olivine crystals in the shape -of 

 a V, is evidence of mass deformation, such as takes place in schists, 

 and is not such as results from the flowing of a liquid magnia, 

 Professor Eenard, however, was uncertain ; his first letter to Pro- 

 fessor Eosenbusch states that he was quite sure that the Serpentine, 

 Peridotite, or Lherzolite — for the rock has been called all three 

 names — was volcanic, a view that Professor Eosenbusch endorsed.! 

 In the Challenger reports, however, he first states that it is volcanic ; 

 but adds in a footnote that he must express himself with more 

 reserve " because recent researches tend more and more to establish 

 the fact that in many cases peridotites are rocks embedded in the 

 schisto-crystalline series, with which they must have a common 

 origin." J Neumayr states that St. Paul's Eocks lie on a line 

 characterised by volcanic eruptions ; this line includes St. Helena, 

 Ascension, St. Paul's Eocks, and the area of frequent submarine 

 volcanic action situated in long. 20-22° E. and lat. 0° 30' S.§ 



Sir A. Geikie supported the volcanic origin of the rock, || and Mr. 

 M. E. Wadsworth attacked Professor Eenard' s interpretation of the 

 microscopical evidence,^ and Professor Eenard replied. ** The out- 

 come of the discussion is represented in Neumayr's acceptance of 

 the non-volcanic origin of the rock, ft though at the same time he 

 recognises that it lies in a volcanic region. 



While the evidence at St. Paul's Eocks is not quite satisfactory, 

 that at Ascension is quite definite. Darwin states %\ that, " In the 

 neighbourhood of Green Mountain fragments of extraneous rocks 

 are frequently met with embedded in the midst of scoriae. They 

 nearly all have a granitic structure, are brittle, harsh to touch, and 

 apparently of altered colours. Darwin's principal finds were : 

 Firstly, a white syenite streaked and mottled with red, consisting 

 of well-crystallised felspar, numerous grains of quartz, and brilliant 

 though small crystals of hornblende. Secondly, a brick-red mass 



* Brit. Assoc, 1885, Aberdeen, Nature, vol. xxxii. p. 582. 



f " Neues Jabrbuch," 1879. 



\ Challenger Eeports, " Petrology of St. Paul's Eocks," p. 15. 



§ Erdgeschichte, Leipzig, 1890, p. 199. 



|| Nature, xxvii., 1882, p. 25. 



ir Science, I., p. 590, 1883. 



** Bui. Soc, " Beige de Microscopie," p. 165, 1883. 



if Deukschr, k.k. Ak. Wiss. Wien. Math.-Nat. CI., Bd.L., 1885, p. 132. 



J} " Geological Observations on Volcanic Islands, " 1851, p 40. 



