36 GEOLOGICAL BIOLOGY. 



Jurassic System. The JURASSIC SYSTEM was originally 

 applied by Brongniart, in 1829,* to the Jura limestone of the 

 Jura Mountains and the associated formations the Lias, thin, 

 regular-bedded argillaceous limestones, known in many places 

 in Europe and England, and the Oolitic rocks, or Oolite, so 

 named on account of its resemblance to the roe of fish (oon, 

 egg, and lithos, stone ; roe-stone). 



This Jurassic system is rich in its Ammonite faunas in 

 Europe. In America the system is not characteristically 

 represented, but in Texas, in the Rocky Mountain area and 

 in California are seen typical exhibitions of the Triassic and 

 Jurassic systems of the American type. 



Cretaceous System. The CRETACEOUS SYSTEM is an expan- 

 sion of the " Chalk formation " to include the system of rocks 

 associated with it ; the Chalk of the shores of the British 

 Channel was described in literature under that name before it 

 became established as the name of a geological division. The 

 Dutch geologist J. J. d'Omalius d'Halloy described as ter- 

 rain cretace' the third division in his geological classification 

 of the secondary strata of northern Europe, in an essay on 

 the geological map of Holland, etc., in i822.f 



His classification of the secondary rocks was as follows: 

 I, terrains peneens (todte-liegende of the Germans); 2, ter- 

 rains ammoneens (the Jurassic); 3, terrains cretace'; 4, masto- 

 zootique (the Tertiary of others) ; and 5, pyroide (for the rocks 

 having igneous origin). Fitton, in 1824,^: grouped together 

 into a continuous series the rocks which were afterward recog- 

 nized as constituting the typical Cretaceous system, but he 

 did not name them at the time. The typical Cretaceous rocks 

 of England and Europe were the Wealden, the lower Green- 

 sand, the Gault, the upper Greensand, terminating with the 

 Chalk. In North America our standard has been determined 

 by comparison of contained fossils, and the typical Cretaceous 



* " Tableau des Terrains qui composent l'6corce du globe," p. 221. 



f " Observations sur un essai de carte geologique des Pays-Bas, de la 

 France, et de quelques contrees voisines": Memoires, etc., Namur, 1828, p. 23. 



\ " Inquiries respecting the geological relations of the beds between the 

 Chalk and the Purbeck limestone in the southeast of England": Ann. of 

 Phil. His., vol. vn. p. 365, 1824. 



