XXIV INTRODUCTION. 



were relatively cool, with -well-marked seasons, seems indubi- 

 table ; and if this is so, the climate must have been notice- 

 ably cooler than that of either the preceding or succeeding 

 periods. 



Regarding the preceding Wealden, Seward (1895, p. 239) 

 writes: "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 to-day." The succeeding Gault and 

 Upper Greensand create the general impression of having beem 

 warmer again, but 1 cannot express an opinion on this till I 

 have completed my examination of the plants of these periods. 



Published accounts of the fossil animals of the Lower Green- 

 sand of England do not support or supplement this conclusion 

 from the plants, for there are remarkably few remains of the 

 kind from which any evidence is deducible. There seems, 

 however, to bo a general impression among some geologists that 

 the Cretaceous climate of England had begun to be cooler by 

 Aptian times. In conversation Dr. Gregory pointed out to me 

 the notable lack of large corals in the Greensand, even in the 

 cherty deposits in which they might lit hologically be expected 

 to be prolific. Land-animals of the period are very few : the 

 famous Maidstone Iguanodon, and two or three other species of 

 reptiles, scantily represented, seem to be all the British records. 

 Dr. Andrews kindly informs me that they afford little or no 

 evidence regarding their habitat. The one specimen which 

 suggests a rather warmth-loving habit is only represented by 

 fragmentary bones, and these may well have drifted or been 

 carried some distance. 



Too little is known of the land-distribution and the direction 

 of the currents, etc., of Aptian Britain to make a discussion of 

 the causes of this cooling (so clearly indicated by the plant- 

 structures) at all profitable. It is evident that the effect of a 

 cooling-off from the warmth of the Wealden must have had 

 a profound effect on the vegetation. 



PREVIOUS KECORDS OF ENGLISH LOWER GREENSAKD PLANTS. 



In 1822 Mantell (p. 78) gives "wood" in the list of the 

 " organic remains " fiom Willingdon, Seimeston, etc., again 



