$04 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



of similar fossil remains in deposits of different geological age 

 but the same lithological character, by referring to the lignite 

 formations below and above the coarse limestone of the Paris 

 basin and in the Isle of Wight. 



Gressly was so strongly impressed with the variability of rocks 

 considered in horizontal succession that he discountenanced 

 the prevailing endeavour to identify in all the other European 

 areas the same palseontological and lithological sequence as had 

 been established for England. In his opinion this fallacious 

 method was preventing the foreign geologists from arriving at 

 a true conception of the characteristics of the Jurassic succes- 

 sion in their own countries. 



The continental study of the Jurassic system received a new 

 impulse when Leopold von Buch published his remarkable 

 memoir, On the Jurassic Rocks in Germany (1839). In short, 

 clear sentences Leopold von Buch sketched the extension and 

 the orographical character of the South German Jura. Above 

 the Lias, which spreads everywhere below the higher Jurassic 

 rocks, the northern edge of the Swabian and Franconian Alp 

 ascends sharply from the plains in front. Isolated Jurassic 

 hills rise amid the plain like island masses. This peculiar 

 configuration, in Buch's opinion, is not a result of a subse- 

 quent movement of elevation or of advanced denudation, but 

 is associated with the conditions under which the Jurassic rocks 

 originated. He compared the present configuration with the steep 

 outer slope of a coral reef> and expressed his conviction that the 

 Swabian-Franconian Alp represents the remains of such a reef. 



The tectonic disturbances, foldings, and anticlines in the 

 Swiss Jura were said by Buch to have been connected with the 

 Alpine upheaval ; the origin of the Franconian Dolomite was 

 traced to the occurrence of a crust-rupture extending parallel 

 with the Bavarian Forest, into which, according to Buch, sub- 

 terranean magnesia vapours escaped, and by chemical inter- 

 change the white limestone in the neighbourhood was converted 

 into dolomite. 



Buch sub-divided the South German Jurassic deposits into 

 three chief groups : 



3. Upper or White Jura. 

 2. Middle or Brown Jura. 

 i. Lower or Black Jura (Lias). 



A short description of each group was given by Buch, 

 and a comparison drawn between the South German strata 



