548 STEVENSON— FORMATION OF COAL BEDS. [November 3, 



tumble in with the rest. Gibbs,-* who saw the spring flood of the 

 Yukon river in Alaska, relates that 



" During tlie liigh stage of water, which lasts for perhaps two or three 

 weeks, great sections of the heavily wooded banks are undermined and 

 swept away. The majestic spruce trees and tamaracks and birches, which 

 covered them, topple over and are swept down by the current along with 

 immense quantities of drift wood from the forest beds. The entire accumula- 

 tion, amoimting to thousands of cords of wood, is discharged into Bering 

 sea, whose restless waves and shifting winds scatter this fuel and pile it on 

 barren shores, hundreds of miles distant." 



The conditions along the Mississippi-Missouri and their tribu- 

 taries are the same ; when the weakened banks cave, the forest, with 

 its fallen trunks and litter, finds its way into the water. The masses 

 of drifted wood in the channels of the Mississippi and some of the 

 streams entering that river from the west have been mentioned in 

 nearly all textbooks on geology during the last seventy-five years ; 

 but in most instances the descriptions have been incomplete, while in 

 some cases they were sufficiently inaccurate to be misleading. 



In the early days, great numbers of waterlogged trees were held 

 back by their roots and were moored in the silt with their usually 

 branchless stems pointing down stream. These were the " snags " 

 which rendered navigation perilous. Fewer of them are encoun- 

 tered now because a very great part of the drainage area is under 

 cultivation, but enough are added annually to necessitate the services 

 of several snag-removing boats along the line of nearly 2,000 miles. 

 Most of the floating stems find their way to the Gulf, but some are 

 stranded on the delta during floods. At one time, however, they 

 were diverted, in chief part, into the Atchafalaya, the first great arm 

 of the river at the head of the delta. 



Darby-^ has told us that the vast ninnber of trees brought down 

 by the Mississippi were thrown into this arm, through which they 

 were carried with tremendous speed. The Atchafalaya raft began 

 to form in 1778, when practically the whole drainage area of the 



="0. Gibbs, "The Break-up of the Yukon," Nat. Geog. Mag., Vol. XVII., 

 1906. pp. 268-272. 



^ W. Darby, ".A. Geographical Description of the State of Louisiana," 

 2d Ed.. New York, 181 7. pp. 131-1,^3. 



140 



