Ch. xxxi] age of the brown coal. 539 



througli them. They coDtaiii numerous impressions of leaves and stems 

 of trees, and are extensively worked for fuel, whence the name of the 

 formation. 



lu several places, layers of trachytic tuff are interstratified, and in these 

 tuffs are leaves of plants identical with those found in the brown-coal, 

 showing that, during the period of the accumulation of the latter, some 

 volcanic products were ejected. 



Mr. Von Decken, in his work on the Siebengebirge,* has given a 

 copious list of the animal and vegetable remains of the freshwater strata 

 associated with the brow^n-coal. Plants of the genera Flahellaria^ 

 Ceanothus, and Daphnogene, including D. cinnamomifolia (fig. 169, 

 p. 191), occur in these beds, with nearly 150 other plants, if we include 

 all which have been named from the somewhat uncertain data furnished 

 by leaves. They aie referred for the most part to living genera, but to 

 extinct suecies. Among the animal remains, both vertebrate and inver- 

 tebrate, many are peculiar, while some few, such as Littorinella acuta^ 

 Desh., help to approximate these strata with some of the upper fresh- 

 water portions of the Mayence basin. The marine base of the Mayence 

 series consists of sandy strata closely allied, in geological date, as we 

 have already seen, p. 190, to the Limburg group, called Upper Eocene 

 in this work. But in regard to the Rhenish freshwater deposits near 

 Bonn, so large a proportion of the plants, insects, fish, batrachians, and 

 other fossils, are such as have been met with nowhere else, that we 

 cannot as yet assign to them a very definite place in the chronological 

 series. They were undoubtedly formed during that long interval of time 

 which separated the Nummulitic from the Falunian tertiary formations, 

 so that they are newer than the Middle Eocene, and older than the 

 Miocene strata of our Table given at p. 104. The classification of the 

 deposits belonging to this interval must still be regarded as debatable 

 ground, very different opinions being entertained on the subject by 

 geologists of high authority. Should a passage be eventually made 

 out from the tertiaries of the north of Germany, on which the labors 

 of M. Beyrich have thrown so much light, to the faluns of the Loire, 

 by the discovery of beds intermediate in age and paleontological char- 

 acters, the best line of demarcation that we can adopt is that pro- 

 posed by M. Hebert, according to which all the Limburg beds, the 

 Gres de Fontainebleau, the lower part of the Mayence basin, and 

 the Hempstead beds of the Isle of Wight (see p. 192), are classed as 

 Lower Miocene, while the Faluns rank as Upper Miocene. Between 

 these formations there is still so vast an hiatus, that I have thought it 

 inexpedient, for reasons before explained, to unite them under a common 

 name.f 



* Geognost. Beschreib. des Siebengebirges am Rhein. Bonn. 1852. 



\ "While this sheet was passing through the press, a valuable paper on the 

 Brown-Coal and other deposits of the Mayence Basin, by William J. Hamilton, 

 Esq., P. G. S., has been published (Geol. Quart, Journ., vol. x. p. 254), in which 

 the question of classification above alluded to is discussed. Whatever termi- 



