■911.] STEVEXSOX— FORMATION OF COAL BEDS. 559 



during the periodical floods. The chff crests are from loto i6o feet 

 above the floodmark and sections show white, yellow and red sands 

 with bluish or variegated clay beds. Ten feet of red clay was seen 

 at the top of one section, while in another are white clays resting on 

 bright red clays. The area studied by Brown is about 400 by 1,000 

 miles. Within this he saw four insignificant exhibitions of vegetable 

 matter in the deposits, which seem to have been laid down in an 

 estuary. 



It is evident that very little of the drifted material is deposited 

 anywhere within the river region or immediately beyond ; the drift- 

 wood deposits on the northern shores, though vast in the aggregate, 

 clearly represent but a small part of the timber brought down by the 

 great northward flowing rivers ; the writer has followed the Gulf 

 Stream for more than 3,000 miles but he has rarely seen floating 

 logs ; in rhe central part of the so-called Sargasso sea of the north 

 Atlantic, he saw no floating timber and captains of steamships 

 familiar with that area have assured him that driftwood is of rare 

 occurrence ; the Orinoco brings down great numbers of trees which 

 should be caught by the westward current, but the writer, during 

 two voyages between Trinidad and Colon, saw not one. \Miat, then, 

 becomes of the vegetable material carried down by the rivers ? 



Deep sea soundings in the Atlantic ocean give no answer to the 

 question. ^Material brought up by the trawl seems to be practically 

 free from vegetable matter. It has been suggested that the constant 

 " creep "' at great depths maintains the supply of oxygen, which 

 under the pressure would be greater than at the surface, so that 

 organic matter would be destroyed. \\'hether or not the explana- 

 tion be in this suggestion, it is certain that where dift'erent conditions 

 of movement and pressure exist, one finds an accumulation of vege- 

 table material on the ocean bottom. The observations by Agassiz^^ 

 in the Gulf of Mexico and the Caribbean as well as in the Pacific 

 off the coast of ^Mexico are final in respect to this matter. His 

 statement is that 



"A. Agassiz, "Three Cruises of the Blake," Bull. Mus. Conip. ZooL, 

 Vol. XIV., p. 291 ; " General Sketch of the Expedition of the Albatross, 

 1901," Vol. XXXIII., p. 12. 



157 



