Prof. J. W. Gregory — Geological Relations of S. Georgia. 63 



would belong to that or some allied genus. Dr. Hinde has kindly- 

 examined the specimen, and says that unless it be a coral it is very 

 difficult to say what it can be. 



Another group of specimens appeared at first sight the most hopeful 

 of determination. They are csespitose organisms, of which one tuft 

 is 90 by 100 mm. in diameter; the branches are, on an average, from 

 3 to 4 mm. in diameter, and they subdivide dichotomously. A section 

 from one specimen shows broken tubuli, which resemble those of 

 monticuliporoids, and the fossil from which this section was cut has 

 a habit similar to that of several genera of Upper Ordovician and 

 Silurian monticuliporoids. 



Another series of specimens consist of long unbranched stems, and 

 as their structure seemed to resemble that of sponges they were sent 

 to Dr. G. J. Hinde. He kindly examined them, but declined to accept 

 them as sponges. 



A few of the South Georgia specimens were sent to Dr. R. S. Bassler, 

 who kindly examined them and showed them to his colleagues in the 

 National Museum, Washington. He tells me that the opinion there 

 formed is in favour of the specimens being either sponges or fucoids. 

 Dr. Bassler remarks that "one of our Ordovician genera, Camarocladta, 

 shows a structure something like these specimens, and for a guess 

 I would say they are nearest this genus. Mr, Ulrich and I agree 

 that they are not Bryozoa, because it is our experience that no matter 

 how great the crushing, specimens preserved as these are show some 

 of the original structure ". He agrees that the age of these fossils 

 is probably later than Cambrian and earlier than Devonian. This 

 conclusion is also supported by a small fragment, which, if found 

 in a graptolitic bed, would be regarded as a piece of a monoprionid 

 graptolite. The specimen has been examined by Miss Macphee, who 

 thinks it is probably a fragment of a graptolite ; and this opinion 

 is shared by several members of the geological school of this University 

 who have had experience in collecting graptolites in our Southern 

 Uplands. "We, however, feel that this fragment is too small for its 

 identification as graptolitic to be anything more than a probability. 



The general evidence, then, of this collection is in favour of the 

 calcareous clay-slates of Mr. Ferguson's Lower Cumberland Bay 

 Series, on the north-eastern coast of South Georgia, being either 

 Silurian or Ordovician, though owing to the imperfect preservation 

 of the fossils this opinion is necessarily doubtful. According to 

 Mr. Ferguson the fossiliferous beds rest unconformably on the Cape 

 George Harbour Series, which would be pre-Ordovician or possibly 

 Ordovician. Mr. Tyrrell's description of these rocks shows, however, 

 that they could not have differed greatly in original composition from 

 those of the Cumberland Bay Series. 



Above the horizon from which Mr. Ferguson obtained his fossils is 

 a thick succession of sediments, which he regards as one continuous 

 series. Interstratified with these rocks are abundant tuffs, and 

 a diabase sill is intrusive in the Lower Cumberland Bay Series. 

 The igneous centre discovered by Dr. Heim further to the south-east 

 may be the source of the volcanic debris iu the Cumberland Bay 

 Series. 



