D. Ferguson — Geology of South Georgia. 53 



its facility for early jointing. I adopt the following as a working 

 hypothesis to guide me in further researches. 



When our Coal-measures were first laid down they would consist 

 of a series of incoherent sands and muds, and this uncompacted 

 condition may have persisted for a very long period, so long as 

 pressures were not excessive and no cementation took place ; even 

 surviving considerable tectonic disturbances, if we may judge by the 

 condition of the Bovej' Tracey Beds. The peats, however, would be 

 subject to changes dependent upon processes entirely innate : the 

 gradual loss of volatile constituents or at least the resolution of the 

 carbon compounds into new groupings and the conversion of 

 the mother-substance of the coal into lignite. This has happened, 

 as Principal Clayden informs me, to the logs and trunks in the 

 Bovey Tracey deposits, and I have observed the same thing in the 

 coaly lenticles at Alum Bay. Professor J. J. Stevenson, in the latest 

 of his brilliant and closely reasoned memoirs on the formation of 

 coal-beds,' cites two instances of Quaternary peats passing into 

 lignite. 



In this condition the coal substance would be brittle and liable to 

 joint. Now, let a deforming stress or strain be applied, or perhaps 

 a wave or tremor sweep the country, and the sheet of brittle material 

 "would be shattered, while the unconsolidated sands and clays would of 

 course be unaffected. 



The idea that the initiation of joints, as it were the pulling of 

 the trigger, is due to seismic tremors is urged by W. 0. Crosby, and 

 at a recent meeting of the Yorkshire Geological Society Mr. Harker 

 remarked that the regularity of the joints in sedimentary rocks 

 favoured the view that they were due to some kind of wave action. 

 In no sedimentary rocks is there greater regularity than in coal. 



I have no desire to press this or any other hypothesis, but I would 

 remark that, though evidence is not lacking of considerable tectonic 

 movements having taken place during the deposition of the Coal- 

 measures adjacent to the Pennine area, it seems to me impossible to 

 connect them with this widespread phenomenon that cuts, at all 

 angles, the lines of structure of the country. 



In conclusion, may I beg for information from those readers of the 

 GicoLOGTCAL Magazine who have opportunities for observing lignite 

 beds occurring in uncompacted sediments regarding the development 

 of cleat. 



II. — The Geologt op South Geoegia.- 



1. jS'otes on the Gkologt of South Georgia. 



By D. Ferguson, Mem. Inst. M.E., F.E.G.S. 



^^'KE island of South Georgia is nine hundred miles S. 80° E. from 

 the Falkland Islands. Tlie coastline of the island is rock-bound 

 and more or less precipitous, and there is neither open beach nor 



\ Proc. Amer. Phil. Soc, Hi, 208c, p. 33. 



" A more detailed account of the geology of South Georgia, and of its rocks 

 and fossils, will appear in one of the volumes on the results of the Scotia 

 Expedition, which are now being published by Dr. W. S. Bruce. 



