288 ANNALS NEW YORK ACADEMY OF SCIENCES 



long period and formed a thick coating of humus, which, torn off by a 

 mighty flood, might be carried into the basin, there to become coal. It 

 has been suggested many times that such removal would be necessary in 

 order to maintain continued growth of the forest, there being something 

 in humus which is repugnant to trees. 



The latter suggestion should be considered first, for it has been urged 

 as showing that the transport doctrine is the necessary explanation of a 

 thick mass like the Bourran bed, almost unbroken by partings. But it is 

 due to a misconception of the conditions. Plants do not find repulsive 

 materials in humus. Almost 150 years ago, De Luc wrote in one of his 

 letters that the old fortifications of Oldenburg, made of material taken 

 from the swamps, were covered with trees showing remarkably luxuriant 

 growth. It is well known that advancing swamps destroy forests by 

 obstructing the drainage, so that the trees are literally drowned by the 

 increasing moisture. There are many plants, among them some trees, 

 which not only endure the moisture, but even thrive in the moist humus ; 

 some indeed attain their best estate only when growing in the humus 

 itself. The cedar of the Xew Jersey swamps, as shown by Cook many 

 years ago, yields its finest wood only where the roots do not reach the 

 subsoil ; for where the swamp is shallow and the roots penetrate the under- 

 lying beds only inferior wood is produced. The vast thickness of appar- 

 ently uninterrupted coal in the Bourran bed is in no sense an argument 

 in favor of origin by transport; on the contrar3^ it may be an important 

 argument against the doctrine as applied to the Decazeville basin. 



The floods, upon which some authors lay great stress, could do little 

 along the lines of the streams, even were the valleys as wide at bottom as 

 are those now crossing the basin. It is true that large streams in flood 

 carry houses and logs, but those are, so to speak, only loose materials lifted 

 from open spaces. Transported trees are merely those which have fallen 

 into the water from undermined banks. But along the streams entering 

 the basin, the amount of vegetable matter available for removal could be 

 in only insignificant quantity. The area with abundance of vegetation 

 was mostly in the forested upland region, which is supposed to have been 

 a rolling surface, ill-drained in portions, with broad rather deep swales 

 in which at times the water would collect and flow with increasing force, 

 these conditions being most favorable for accumulation of humus or half- 

 decayed vegetable matter. This humus cover on the upper surfaces could 

 not be affected by the moving waters : the only spaces to be considered are 

 the lower broad hollows falling toward the streams, through which the 

 mass of water would tend to flow rapidly. 



One must recognize that the conditions observed in floods of the Seine 



