THE GEOLOGICAL RELATIONS AND SOME FOSSILS OF SOUTH GEORGIA. 819 



figs. 4, 5, 6). They grow in rather matted tufts (fig. 4), of which the branches 

 divide repeatedly and are about from a half to 1 mm. in diameter. They appear 

 to be similar in nature to the stouter specimen shown in fig. 2. 



Camarocladia was founded by Ulrich and Everett # on some tufted fossils from 

 the sponge bed at the base of the Trenton Limestone (Middle Ordovician) at Dixon, 

 Illinois. The internal structure is poorly preserved, but some of the canals through 

 it are similar to, though far more crowded than, those in the South Georgian speci- 

 mens. Ulrich and Everett's figures do not show the transverse partition of some 

 of the South Georgian specimens, but as those authors described Camarocladia as 

 allied to Peronetta or Verticillites, the presence of this structure increases the 

 resemblance to Verticillites, if they used that genus to include Tremacystia. 



The type species of Camarocladia, C dichotoma, consists of branches about 

 " 2 mm. or a little more in diameter," which subdivide at intervals of about 

 10 mm. ; and these dimensions would agree with those of the thinner stems in the 

 specimen shown in fig. 2. C. dichotoma was found with specimens which Ulrich 

 and Everett regard as probably representing three other species ; one of these was 

 smaller and more branched than C. dichotoma, . while the other two were more 

 robust. As the fossils shown in figs. 4, 5, and 6 have an average diameter of less than 

 1 mm., they might represent the smallest of the Illinois species; while the tufted 

 forms shown in fig. 2, in which the branches vary from 3 to 4 mm., and the rarely 

 branched form shown in fig. 3, of which the branches are 5 to 6 mm. in diameter, 

 would represent the more massive Illinois species. 



The fact that these fossils, both in Illinois and South Georgia, have a similar range 

 in size may be a worthless coincidence. 



The South Georgian specimens cannot be claimed as presenting anything more 

 than a considerable resemblance to Camarocladia, and that name is therefore only 

 provisionally adopted for them for convenience of reference. 



The Ordovician or Silurian age of these Camarocladoid fossils is 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 M. 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. 



Two further types of fossils are included in the collection, but their evidence as to 

 the age of the rocks is also ambiguous. One fossil (Plate XCII, fig. 7) is an irregularly 

 branched tuft, which seems to me probably a sponge. The other is a well-marked 

 dichotomous organism with branches of usually from 3 to 5 mm. across, and with a 



* Geol. Surv. Illinois, vol. viii, pt. ii, Paleontology, Sect. 5, "Descriptions of Lower Silurian Sponges," 1890, 

 pp. 280-1, pi. vii, fig. 1. 



