INTRODUCTION. 2$ 



coal-seams in the open air workings of Commentry, the details of which are 

 given by de Lapparent \ quite agrees with Grand' Eury's description of the 

 extreme case of allochthony. 



Grand' Eury's conception of the matter is essentially as follows. Coal- 

 seams were formed in broad land-locked lake-basins (lagoons) surrounded 

 by wooded swamps, in which the decaying vegetation softening and rotting 

 as it lay on the ground produced in time a layer of matter of vast thickness. 

 The water of frequent rain-storms running slowly off in trickling streams 

 gradually carried away with it the softened wood in shreds from inside the 

 encasing rind, which was itself ultimately broken up and conveyed with 

 other deposits into the basin. Here the processes which lead to the forma- 

 tion of coal took the place of decay, the mass of the coal being produced 

 from the rind, while the particles of softened wood were converted into 

 fibrous coal. The masses of aquatic and marsh plants, which covered 

 the surface and margins of the basins with their luxuriant growth, also 

 supplied their contingent in the form of the parts which died and sank to 

 the bottom. 



We know that stumps of trees, the remains of former forests, are found 

 here and there in coal-deposits, either singly or in groups, and in their 

 natural position. One of the best known cases is that of the fossil Sigillaria- 

 forest discovered by Goldenberg 2 during the construction of a tunnel on the 

 railway from Saarbriicken to Neunkirchen. Grand' Eury gives many 

 instances from the Coal-measures of Central France, which were brought to 

 view by the opening of stone-quarries, and in which the chief growths were 

 Psaroniae, Calamodendrae, and Cordaitae ; and though Fayol 3 is of opinion 

 that these plants did not grow where they now stand, but were torn up and 

 floated away and assumed the erect position in the water, it would appear 

 that this may have happened in single cases but can scarcely be true of the 

 whole of the phenomena which have to be considered. England also 

 furnishes numerous examples. It is natural to assume from these cases that 

 coal was formed in wooded swamps. But Grand' Eury points out that if 

 this were the case, we should often find such stumps lying across the seams, 

 with their lower extremity, their roots, immersed in them. The first case 

 does actually occur, but it is so extremely rare that Grand' Eury 4 can only 

 cite three or four instances. Elsewhere the stumps are as a rule cut square 

 off at the bottom of the seam, and they end in the same way where they 

 reach decided fissures in the stratification. Moreover they never root in the 

 coal, but only in the beds of stone which form the roof of the seam, even 

 where they occur close above the seam itself. The coal therefore does not 

 in fact lie in the same spots with the trees ; where they grew, no coal 



1 de Lapparent (1), vol. ii, p. 864. 2 Goldenberg (1). 3 Compare de Lapparent (1), 



vol. ii, p. 863. * Grand' Eury (2), p. 1 78. 



