I NT ROD UCTION. 1 9 



But with this general idea of the process in question we are still far 

 from having a thorough understanding of it. On the contrary we are con- 

 fronted with a succession of new doubts. There is the question often raised by 

 the earlier authors, where the plants grew whose remains we now see gathered 

 together into coal-seams. The question has been answered in more than one 

 way. Some have thought that coal was formed in the sea by the accumu- 

 lation of sea-weeds, but this view was soon set aside by further investigation. 

 Others, as Count Sternberg and Boue, appealed to the trunks of trees in the 

 Mississippi, and conceived of masses of drift-wood accumulated by mighty 

 rivers. Giimbel l named this view the theory of allochthonous origin. 

 Others again have sought a probable explanation of the matter by a com- 

 parison with our present peat-bogs and made the entire material of the 

 coal-seams grow in loco, adopting therefore the theory of autochthonous 

 origin. This view was defended in the eighteenth century by Beroldingen 

 and de Luc, and it was accepted with gradually increasing decision by most 

 of the eminent geologists and palaeontologists, especially by A. Brongniart 

 and Elie de Beaumont 2 ; it was completed and put into consistent shape by 

 Goppert 3 , and Unger 4 accepted his ideas with some reservations. The 

 view intermediate between these two, that the mode of formation varied as 

 in the case of the lignites and was sometimes allochthonous, sometimes 

 autochthonous, also makes its appearance with more or less distinctness, 

 especially among the older autochthonists. Goppert opposed this theory 

 in the most decided manner, repeatedly pointing to the extraordinary 

 uniformity in the layers of coal in all parts of the world. We shall see 

 presently that it has recently reappeared with certain reasonable limitations 

 under the auspices of Grand' Eury 5 . 



Goppert 6 and Unger 7 , and before them Lindley and Hutton 8 , adduce 

 many weighty arguments to show that the assemblage of phenomena pre- 

 sented by the seams of coal cannot be explained by the assumption of an 

 allochthonous origin. On this assumption, says Goppert, it is inconceivable 

 that the coal-seams should cover such enormous spaces in beds that are 

 everywhere alike and are of equal size, and again that coal should be so 

 homogeneous and so pure in quality that it is rare to find fragments of 

 stone inclosed in it. For every stream that was to carry along with it so 

 much vegetable matter must have been strong and rapid, and would have 

 carried down at the same time mud, sand, and gravel. We should therefore 

 expect to find in the seams a regular alternation of coal and inorganic 

 material. But this has not been observed anywhere ; a comparison with 

 the composition of living plants shows at most a considerable increase in 

 the ash-constituents, but this is quite intelligible if we take into considera- 



1 Giimbel (2). 2 Grand' Eury (2). 3 Goppert (14). * Unger (6). 



8 Grand' Eury (2). Goppert (14). T Unger (6). 8 Lindley and Hutton (1). 



C 2 



