THE GEOLOGICAL RELATIONS AND SOME FOSSILS OF SOUTH GEORGIA. 821 



of these rocks, " now so well known from older Palaeozoic rocks in different parts of 

 the world, suggests the possibility of the existence of rocks of high antiquity either 

 on Dundee Island or within the iceshed of that region. But the specimen itself 

 furnishes no satisfactory evidence of its geological age." # 



The evidence against the subdivision of the Cumberland Bay Series is that, 

 according to Mr Ferguson, it is all one continuous conformable sequence, and the 

 rocks have so many features in common that they must have accumulated under 

 similar conditions. Each division, as shown by Mr Tyrrell's description of the 

 rocks, includes bands of tuff and layers containing radiolaria ; and all these divisions 

 are cleaved, though the rocks of the lower division are much more sheared and 

 altered than those in the two upper divisions. The whole of the Cumberland Bay 

 Series appears to have been formed off the shores of a volcanic land, which included 

 some sedimentary rocks, the debris of which formed the grits and greywackes. 



Nevertheless the lithological and stratigraphical evidence for the unity of the 

 Cumberland Bay Series is not conclusive. One of Mr Ferguson's photographs 

 shows the middle division of the Cumberland Bay Series in apparent uncon- 

 formity to the lower division, but Mr Ferguson explains that the photograph 

 is deceptive. However, he remarks that the relations of the middle and lower 

 divisions of the Cumberland Bay Series in an adjacent locality would be explained 

 by an unconformity ; and their relations as shown on his map and the overlap 

 of the middle division on to the Cape George Series at Cape George Harbour and 

 elsewhere in that district are facts in favour of an unconformity at the top of the 

 lower division. 



The lithological resemblance of the three divisions is not convincing ; because if 

 the two upper divisions were formed from the denudation of the lower division, 

 supplemented by material from an older common source, the rocks would naturally 

 be similar in composition ; and the presence of radiolarian beds in the three divisions, 

 in the absence of evidence that the radiolaria all belong to the same fauna, may be 

 explained as due to their deposition under similar conditions. The radiolaria found 

 in the Lower Cumberland Bay Series are too imperfect for identification, and it may 

 be that, in spite of a general similarity in aspect, they may belong to an older fauna 

 than those in the upper divisions of that series of rocks. The presence of radiolaria 

 in all three divisions is, however, in favour of the conclusion which Mr Ferguson 

 appears on the whole to favour, that the three divisions of the Cumberland Bay 

 Series are one conformable sequence. 



I have more than once tried to interpret the fossils from the lower division as 

 Mesozoic, by comparing them with Cerioporoid bryozoa or Mesozoic calcareous 

 sponges, but without success ; and though it must be recognised that opinions based 

 on such uncertain fossils are hazardous, the fossils seem to me pre-Devonian. 



* A. Geikie, " Notes on some Specimens of Rocks from the Antarctic Regions ; with Petrographical Notes by 

 J. J. H. Teall, F.R.S.," Proc. Roy. Soc. Edin., vol. xxii (1897-1899), 1900, p. 67. 



TRANS. ROY. SOC. EDIN., VOL. L, PART IV (NO. 24). 116 



