CONCLUSIONS. 239 



shallow water, and the fossils embedded in the strata were 

 derived from a wide area, embracing localities rich in both 

 ferns and gyrunosperms. The petrological nature of (<#) and the 

 absence of cycads suggest deeper water ; while the fine blue clay 

 of (b) may have been derived from rocks in an area characterized 

 by the predominance of cycads. It would, however, be difficult to 

 reconstruct the conditions of growth of the several plants without 

 a very careful examination of the rocks and their fossil contents, 

 and at best our conclusions would probably not possess any great 

 scientific value. 



In an old work by linger, 1 we read that in the Wealden period 

 there were " small wet islands, covered with forests, inhabited by 

 the largest and most terrible monsters of the primitive world. 

 The atmosphere was filled with moist vapour, and carbon dioxide 

 exhalations favourable to the prodigious propagation of the 

 amphibian race, and to the development of ferns, cycads, 

 conifers, and some monocotyledons." He goes on to say that 

 "La triste sauvagerie de cet interieur de foret est encore redoublee 

 par celle de ses habitants, parmi lesquels le gigantesque Iguanodon 

 a crete osseuse et la monstreux Hylaosaurus tiennent la premiere 

 place." 



In a more recent monograph on the Wealden period, Schenk 2 con- 

 fidently speaks of the climate as undoubtedly tropical, and refers to 

 the occurrence of tree ferns, the abundance of cycads, and other facts 

 in support of this conclusion. It would be extremely difficult, 

 or indeed impossible, to give any approximate estimate of the 

 temperature in Northern and Central Europe during the Wealden 

 period. The general characters of the vegetation would certainly 

 seem to point to a tropical climate, and there can be little doubt 

 that the temperature was considerably higher than the Wealden 

 districts enjoy at the present day. 



In discussing the climate of a past age, in which no living species 

 of plants existed, and in attempting to make use of fossil plants 

 as indices of climatal conditions, we have to bear in mind the 

 great danger of drawing conclusions from a comparison of extinct 

 and living forms. It is superfluous to point out the lesson so 

 clearly taught by recent plants, that closely allied species frequently 



1 linger, p. 29. 



2 Palaeontographica, vol. xix. p. 256. 



