THE JURASSIC PERIOD. 237 



the whole, constitute the most marked feature of the Jurassic 

 vegetation, many genera of this group being known (Ptero- 

 phyllum, Otozamites, Zamites, Crossozamia, Williamsonia, Buck- 

 landia, &c.) The so-called "dirt-bed" of the Purbeck series 

 consists of an ancient soil, in which stand erect the trunks of 

 Conifers and the silicified stools of Cycads of the genus Mantel- 

 lia (fig. 1 60). The Co-nifera of the Jurassic are represented by 

 various forms more or less nearly allied to the existing Arau- 

 caria; and these are known not only by their stems or 

 branches, but also in some cases by their cones. We meet, 

 also, with the remains of undoubted Endogenous plants, the 

 most important of which are the fruits of forms allied to the 

 existing Screw-pines (Pandanea}, such as Podocarya and Kaida- 

 carpum. So far, however, no remains of Palms have been 

 found; nor are we acquainted with any Jurassic plants which 

 could be certainly referred to the great " Angiospermous " 

 group of the Exogens, including the majority of our ordinary 

 plants and trees. 



Amongst animals, the Protozoans are well represented in 

 the Jurassic deposits by numerous Foraminifers and Sponges; 

 as are the Calenterates by numerous Corals. Remains 



Fig. 160.Mantellia (Cycadeoidea) megalophylla, a Cycad f rom the Purbeck 

 "dirt-bed." Upper Oolites, England. 



of these last-mentioned organisms are extremely abundant 

 in some of the limestones of the formation, such as the 

 " Coral-rag " and the Great Oolite ; and the former of these 

 may fairly be considered as an ancient " reef. " The Rugose 

 Corals have not hitherto been detected in the Jurassic rocks ; 

 and the " Tabulate Corals, " so-called, are represented only by 

 examples of the modern genus Millepora. With this excep- 

 tion, all the Jurassic Corals belonging to the great group which 

 predominates in recent seas (Zoantharia sclerodermata) ; and 



