DICOTYLEDONOUS PLANTS. 381 



This third great change in the vegetable kingdom is 

 considered to supply another argument in favour of the 

 opinion, that the temperature of the Atmosphere, has gone 

 on continually diminishing from the first commencement of 

 hfe upon our globe. 



The number of species of plants in the various divisions 

 of the Tertiary strata, is as yet imperfectly known. In 

 1828, M. Ad. Brongniart considered the number then dis- 

 covered, but not all described, to be 166. Many of these 

 belonsinff to Genera at that time not determined. The 

 most striking difference between the vegetables of this and 

 of the preceding periods is the abundance in the Tetiary 

 series, of existing forms of Dicotyledonous Plants and large 

 trees, e. g. Poplars, Willows, Elms, Chestnuts, Sycamores, 

 and many other Genera whose living species are familiar 

 to us. 



Some of the most remarkable accumulations of this vege- 

 tation are those, which form extensive beds of Lignite and 

 Brown-coal.* In some parts of Germany this Brown-coal 

 occurs in strata of more than thirty feet in thickness, chiefly 

 composed of trees which have been drifted, apparently by 

 fresh-water, from their place of growth, and spread forth 

 in beds, usually alternating with sand and clay, at the bot- 

 tom of then existing lakes or estuaries. 



The Lignite, or beds of imperfect and stinking Coal near 

 Poole in Dorset, Bovey in Devon, and Soissons in France, 

 have been referred to the first, or Eocene period of the Ter- 

 tiary formations. To the same period probably belongs 

 the Surturbrand of Iceland, (see Henderson's Iceland, vol. 

 ii. p. 114.) and the well-known examples of Brown-coal on 

 the Rhine near Cologne and Bonn, and of the Miesner 

 mountain, and Habichtswald near Cassel. These forma- 

 tions occasionally contain the remains of Palms, and Pro- 

 fessor Lindley has lately recognised, among some speci-- 



* See an admirable ailicle on Lignites by Alexandre Brongniart in ths 

 26th vol. of the Dictionnaire des Sciences Naturelles. 



