THE PETROLOGY OF SOUTH GEORGIA. 835 



[Postscript, December 8, 1914. — Mr Ferguson has recently received a new 

 collection of twenty-seven specimens of rocks from the extreme south-eastern 

 end of South Georgia. Both igneous and sedimentary types are represented in 

 this collection. Amongst the igneous rocks are a few specimens of ancient 

 acid lavas and intrusions. Many of these have suffered extreme epidotisation, 

 but can still be recognised as felsites and quartz-trachytes. One or two specimens 

 are still comparatively fresh, especially a spherulitic felsite from Larsen Bay. 

 These rocks occur in Larsen Bay, Slosarczyk Bay, and along the coast between 

 the last-mentioned locality and Cape Disappointment. With this acid series may 

 perhaps be associated an alaskite from Cooper Island, using the term alaskite to 

 denote a granitic rock practically free from ferromagnesian constituents. The re- 

 maining igneous rocks comprise some fresh ophitic dolerites, which occur in all the 

 above-mentioned localities, and probably form a series of dykes and sills. A compact 

 basalt from the coast between Cape Disappointment and Slosarczyk Bay may repre- 

 sent the contact-facies of one of these dolerites. 



The sedimentary rocks include a siliceous slate from the coast between Cape 

 Disappointment and Slosarczyk Bay, fine-grained quartzites from Drygalski Bay 

 and Larsen Bay, and a hornfelsed shale from Slosarczyk Bay. There are also 

 specimens of quartz-veins in phyllite from Cooper Island and the coast between 

 Slosarczyk Bay and Cape Disappointment. From this locality a fragment of a 

 lenticle of crystalline limestone in phyllite was collected. 



Whilst this new collection widens the range of rocks now known in South 

 Georgia, and introduces new problems, it does not appear to invalidate the general 

 conclusions drawn from the study of Mr Ferguson's original collection. The igneous 

 rocks described above probably belong to Heim's " altvulcanischer " area of the south- 

 eastern part of South Georgia. The phyllite with quartz-veins and limestone lenticles 

 probably represents the lower part of the Cumberland Bay Series or the underlying 

 Cape George Series, but the quartzites are unlike any of these rocks as yet described, 

 and may belong to a different series. — G. W. T.] 



TRANS. ROY. SOC. EDIN., VOL L, PART IV (NO. 25). 119 



