CHAPTER XIII 



THE JURASSIC SYSTEM 



A. NOMENCLATURE AND DIVISION 



IN the early days of Geology part of this system was called the 

 "Oolitic Series" (by Conybeare and Phillips in 1822) from the 

 prevalence of oolitic limestones in the central and upper parts of 

 the system in England, and the Lias was described as a separate 

 series ; but on the Continent the equivalents of the former were 

 called the "Jura limestones" by Brongniart and Bou4 in 1829 

 from the fact that beds of this age form the entire range of the 

 Jura Mountains between France and Switzerland. In Germany 

 the name "Jura" was adopted by von Buch for the whole system 

 (1839), who divided it into Lower, Middle, and Upper Jura, and this 

 nomenclature is still used in that country. It appears to have 

 been d'Orbigny (1840-46) who first applied the term "Terrain 

 Jurassique " to the whole succession, including the Lias ; and at the 

 same time he divided the system into a number of stages, but did 

 not group these into series as von Buch had done. 



The arrangement now generally adopted is a division into three 

 series, which are practically those of von Buch, and a further sub- 

 division into stages for which we in England have used local 

 English names, while French geologists employ the latinised 

 names proposed by d'Orbigny with some additions to their number. 

 As a matter of fact it would be more convenient, and more in 

 .accordance with the nomenclature of older systems, to employ 

 latinised names for the three great series themselves. 



The English and French subdivisions are shown in the following 

 table : 



a For the Lower Series the -m Lias or Liasian is already in general use ; 

 for the Middle Series I lonj proposed J the name Glevanian from the 



Eoman name of Gloucester, . at of Clavinian for the Upper Series from 



the Roman name of Weymo' 



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