THE JURASSIC PERIOD 



227 



Lode Belt" of the Sierra Nevada occur in Jurassic and older 

 slates. 



In California, also, important quicksilver deposits occur in 

 metamorphosed Jurassic and later rocks. 



Coal beds of some importance are found, mostly in the Lower 

 Jurassic, in Hungary, various parts of Asia, and Australia. 



As already mentioned, the famous Solenhofen lithographic 

 stone of Bavaria is of Jurassic age. 



Life of the Jurassic 



In Europe, as would be expected because of the great sea trans- 

 gression, the marine life was prolific, and a wonderfully rich record 

 has been left and care- 

 fully studied by many 

 paleontologists. Some 

 idea of the profusion 

 of marine organisms 

 may be gained from 

 the fact that more than 

 4000 species are known 

 from the British Isles 

 alone. The far less com- 

 plete American marine 

 record is in harmony 

 with the adverse phys- 

 ical conditions. 



Beside the marine 

 fossils, the wonderful 

 records of land animals, 

 especially the remark- 

 able and now extinct Mesozoic Reptiles, are worthy of particular 

 mention. 



Plants. — Viewed in a broad way, the plants of the Jurassic 

 were much like those of the preceding period, though some pro- 

 gressive evolutionary changes took place. Ferns, Equisetce, 

 Cycads (Figs. 135, 136, 137), and Conifers continued to be the domi- 

 nant forms, with the Cycads attaining their culmination in both 

 number of individuals and species. The Conifers took on a more 

 modern aspect. The flora appears to have been remarkably uni- 

 form over wide portions of the world. 



Fig. 136 

 A fossil Cycad tree trunk, Cycadeoidea pulcher- 

 rima. This is a Lower Cretaceous species. 

 (After Darton and W. S. Smith, U. S. Geo- 

 logical Survey, Folio 108.) 



