of Geological Periods, 265 



number of facts which A. Erongniart had indicated in his earlier 

 works, and subsequently extended and coordinated in his 'Ta- 

 bleau des Genres de Vegetaux fossiles/ in which the views 

 adopted by the author are marvellously condensed. This re- 

 markable work shows clearly what, previously to the investiga- 

 tions of the last twenty years, was the state of the question with 

 which we are now occupied. 



At that date, on starting from the existing epoch to penetrate 

 into the past, there were observed, first, in the newest portion 

 of the tertiary age, the arborescent genera which still charac- 

 terize the northern temperate zone, represented by species not 

 very different from ours, but still so far distinct from these that 

 the idea of attributing them to an order of things different from 

 ours might be adopted without inconvenience. This first totality 

 underwent but little change in passing from one place to another; 

 and, in examining a deposit slightly older or more recent, there 

 was always nearly the same repetition of forms. However, the 

 observations were still recent, the concordance very vague, and 

 the number of undetermined species very considerable; and it is 

 evident that the presence of the indigenous genera was more 

 easy to seize and verify than that of the exotics, which were 

 most frequently left in the shade for want of the power to de- 

 termine them. It was therefore very natural to draw, from the 

 preponderant existence of the former, the conclusion that the 

 temperature of the period at which they lived did not differ 

 sensibly from that which still prevails under the same latitudes. 

 In this respect the first observations presented a coincidence 

 sometimes due to chance. It will be sufficient for me to cite 

 Armissan, where M. Brongniart, in 1829, indicated a birch, a 

 witch-elm, several pines, a Smilax, a moss, and the fructification 

 of a fern similar to that of Osmunda — a result which certainly 

 did not denote any diversity in the nature of the climate of that 

 locality in comparison with what it is at present, but a result 

 very different from that to which I have since been led by the 

 profound study of the same flora. 



Thus, towards the middle of Tertiary time, the changes ob- 

 served in the vegetation were easily explained by means of ex- 

 amples derived from certain parts of North America, where there 

 was still to be seen an assemblage of most of the genera which 

 could then be indicated in ancient Europe. The aspect of affairs 

 was changed, however, on quitting the middle for the lower 

 Tertiary times. Palms were then met with, at first rarely, then 

 in increasing number. The impressions of the fronds of these 

 plants early attracted attention by their well-marked character ; 

 and at an early period, also, they were regarded as the indication 

 of a climate hotter than ours. The European genera not being 



