498 



PAL/EOBOTANY. 



is called, of the Purbeck beds, consists of an ancient soil, in 

 which stand erect the trunks of Conifers and the stems of 

 Cycads of the genus Mantellia (fig. 394). The fronds of 



Fig. 394. Mantellia (Cycadeoidea) megalophylla, a Cycad from the Purbeck 

 "dirt-bed." Upper Oolites. 



Fig. 395. Coniopteris Murravana. Great Oolite. 



Cycads occur also in great abundance in various Jurassic 

 strata, especially in the lower portion of the series ; and the 



