PALEONTOLOGY. 369 



monographic description of a large part of the Cryptogams. 

 Nevertheless, the unfinished work created a model of the best 

 methods of palaeophytological investigation. 



Although an adherent of Cuvier's theory, Brongniart pointed 

 out the gradual development of the floras in successive geo- 

 logical periods, and thought that the atmosphere, which had been 

 in the earliest epochs warm and moist and supersaturated with 

 carbonic acid gas, became purer and colder in course of time, 

 and less suitable for the lavish development of vascular crypto- 

 gams. According to Brongniart, plant-life began on small 

 islands in the primaeval ocean ; these islands afterwards 

 united to continents, and the vegetation that spread over 

 them always progressed towards more perfect types, and 

 approached more nearly to the flora of the present epoch. 

 He thought that the great changes in the floras and faunas of 

 past ages had been effected contemporaneously by stupendous 

 revolutions. 



Peculiar results were obtained by J. Lindley and W. Hutton 

 in their study of the fossil flora of Great Britain. Their un- 

 finished work, consisting of three octavo volumes, was published 

 between 1831 and 1837, a d contains good descriptions and 

 illustrations of most of the Carboniferous types. Both authors 

 contest the existence of tree-ferns in the Carboniferous forma- 

 tion, doubt the relationship of the Calamites to the Equisetacese, 

 and are of opinion that the Carboniferous flora included not 

 only Conifers, but Cacti, Euphorbias, and other dicotyledons. 

 They altogether deny a progressive development of the fossil 

 floras. 



Brongniart and his predecessors had identified the fossil 

 forms exclusively from microscopic features : the finer 

 structures came little into consideration, A new field of 

 research was opened by several papers which gave an account 

 of the microscopic structure of wood. One of the earliest was 

 an essay by Sprengel (1828) on the silicified stems of trees 

 (Psaronites). This was followed in 1831 by Witham's treatise 

 on the structure of fossil and recent woods, and in 1832 by 

 Cotta's richly illustrated work on the tree-ferns (various species 

 of Psaronius) from the Red Underlyer or Lower Dyassic rocks of 

 Saxony. An important work was published by August Corda 

 between the years 1838 and 1842 on the comparative structure 

 of fossil and recent stems. The illustrations of this work were 

 admirably drawn by the author himself. The memoir in 1839 



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