262 A. J. Jukes-Browne — The Bovey Deposits. 



which are piled over one another in huge masses (none of them stand 

 upright) and which every here and there stretch their branches and 

 roots in the layer of clay which has covered them up, have apparently 

 been floated hither, not only from the immediate circuit of hills, but 

 doubtless also from greater distances. Such a mass of timber could 

 hardly have been furnished by the former. Accordingly, we learn 

 from the structure of these lignite beds that they did not originate 

 in a Tertiary peat-deposit, but from a colluvies of wood uniting in 

 a lake." 



From the above quotation it is evident that Heer supposed the 

 only alternatives to be either the transport of driftwood into an open 

 lake or the growth of moss in a peat-bog ; but there is a third and 

 much more probable method of accumulation, and that is the growth 

 of a forest swamp, like the Great Dismal Swamp of Virginia. 



Heer himself admitted (on the same page) that " the entire absence 

 of freshwater shells, and indeed of aquatic animals generally, is 

 certainly very extraordinary ; and so is the absence of fruits of Chara, 

 which abound elsewhere in Miocene freshwater deposits ; the 

 Nymphaa seeds, however, afford positive proof of fresh water". He 

 thought that the absence of bog plants might be explained on the 

 supposition that these lignites were formed in the middle of the lake 

 and that the bog plants would not have drifted so far out. 



It is now known, however, that the picture of the forest flora given 

 by Heer was based on imperfect information, and that his identifications 

 of some of the plants were not correct. If we turn to the accounts 

 given by Pengelly of the actual composition of some of the lignite beds, 

 and interpret them by the light of more recent knowledge, we shall 

 obtain a rather different idea of the flora, and a very different con- 

 ception of the conditions under which it grew and flourished. 



Pengelly states that the bed of lignite numbered 7 in his section, 

 occurring at a depth of 20J feet from the surface and having a thick- 

 ness of 15 inches, was a matted mass " composed of the coniferous 

 tree Sequoia Coutsim and of the fern Pecopteris lignitum''\ 



Of the twenty-fifth bed, which includes over 6 feet of lignite, he 

 says " the lowest 3 inches of the bed is commonly a mat of 

 fragmentary fronds of Pecopteris ligniUt,m and Lastrea stiriaca, the first 

 being the most prevalent. Above this lie the rhizomes [which 

 Dr. Croker had called * flabelliform leaves ' j in a continuous band 

 about 6 inches thick. . . . The uppermost portion of the bed 

 consists of slabs of 'board coal' of great length, and of a width 

 indicating the existence of trees fully 6 feet in diameter. Bodies 

 occur in this bed having the appearance of roots, with rootlets passing 

 into the clay below ". 



The twenty-sixth bed is a brown clay 2 feet thick, but has "an 

 almost continuous band of broken lignite at the base " which consists 

 of branches of Sequoia Coutsice and a number of dicotyledonous leaves. 



The forty-sixth bed, at a depth of over 96 feet, is a band of lignite 

 only 9 inches thick, but abounding in the small seeds named Carpolithes 

 nitens by Heer. These seeds " are thickly sti'ewed over the surfaces 

 of the laminae of lignite, and slightly embedded in them, as if the 

 latter had been soft when the deposit was formed ". 



