440 SCIENCE PROGRESS. 



been quoted as possible parallels to those of the coal age. 

 M. Rigaud looks to the pitch lake of Trinidad and similar 

 places as the nearest representatives to-day of Coal- Measure 

 conditions ; Lyell and others have referred to the great 

 Dismal Swamp of Virginia as the most accurate picture of 

 coal forests and the accumulation of plant ddbris. An inter- 

 esting account of this famous North American region has 

 lately been published in one of the annual reports of the 

 United States Geological Survey. 1 The upholders of the 

 drift theory, as propounded by Fayol, point to the delta 

 deposits of the Mississippi and other rivers, which transport 

 enormous masses of vegetable material ; and a more recent 

 writer, Ochsenius, calls special attention to the Pemisco lake, 

 and other similar sheets of water in close connection with the 

 Mississippi channel, as very likely places for coal building. 

 Lyell's description of the Mississippi 2 and its drifted rafts of 

 timber enables us to realise at least one possible manner of 

 vegetable accumulation in a delta deposit, or in lagoons 

 bordering the main stream. The well-wooded swamps on 

 either side of the river banks serve to filter off the coarser 

 materials from the overflowing waters in the flood seasons, 

 thus allowing the finer muddy sediment to be carried for a 

 greater distance, and spread out as "a stiff unctuous black 

 soil which gradually envelops the basis of trees growing on 

 the borders of the swamp ". Grand' Eury's view of a short- 

 distance transport necessitates a state of things very difficult 

 to parallel at the present day. Stur, Lesquereux, and 

 others, regard the coal beds as Palaeozoic peat formations, 

 and, arguing from this analogy, Neumayr maintains the pro- 

 bability of a temperate rather than a tropical climate during 

 the Permo-Carboniferous epoch. It is easy to recognise in 

 many river deltas conditions similar to those which doubt- 

 less obtained during the deposition of beds of cannel coal 

 and other carbonaceous sediments, which bear clear indica- 

 tions of subaqueous formation. Some of the widespread 

 sheets of fairly pure coal may probably be best explained by 

 some such concurrence of conditions as Grand' Eury has 



1 Shaler. 2 Lyell (2), vol. i., chap. xix. 



