126 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



As an extreme case, and particularly with reference to the distribu- 

 tion of animal life in the Mgesm, it was suggested that the elevation 

 which produced this desiccation might have amounted to 200 or 300 

 fathoms. I am not aware that, under favourable circumstances, 

 there is anything to prevent a change even as great as this taking 

 place ; but, with reference to the particular epoch under considera- 

 tion, it must be admitted that the igneous force which, along the 

 lines of eruption, produced only such comparatively diminutive chains 

 as those of Mont Pilas (Forez), Cote d'Or and the Erzgebirge*, could 

 scarcely have been adequate to raise so extensive an area as the 

 part of Europe then covered by the Jurassic ocean to the height 

 above mentioned. This branch of the hypothesis need not be aban- 

 doned, however; for, in the first place, the depth of the ocean at the 

 period referred to may not have been very considerable, and indeed, 

 unless subsidence of the bottom had taken place to an enormous 

 extent during the Jurassic epoch, the accumulation of strata must 

 have greatly diminished its profundity. Secondly, the phsenomena 

 do not require that the desiccation should have extended to the zero 

 of marine existence, since there are many species recorded as com- 

 mon to the Jurassic and Cretaceous systems f; and although the 

 number of these may decrease under a more rigid examination than 

 has yet been bestowed on them, others will as surely be found, 

 either among the unpublished fossils now scattered through various 

 collections, or in the rocks themselves, to supply their places. 



Igneous action, the eruptive effects of which are visible in the 

 Crimea, the Caucasus, &c., is regarded also as the agent which has 

 " heaved up in broad horizontal masses, to the different levels at 

 which we now find them, the beds of the former great Caspian Sea" 

 (p. 324). In the event of an oceanic submergence of the region, 

 these elevated "older" and "younger" deposits would each be 

 directly overlaid by the same marine strata which covered the more 

 recent sediments of the basin ; just as, in many localities towards 

 the interior of England, the Purbeck beds at Quainton, Bucks, the 

 Hastings sandt(?)j and elsewhere the Weald clay, are severally 

 succeeded by the lower greensand. 



Except in those cases where denudation appears to have taken 

 place, the absence of the Hastings sand and Weald clay between 

 the Purbeck beds and lower greensand must be referred to the 

 operation of the same cause which has prevented the deposition of 

 *' younger" and recent strata over certain tracts of the "older" 

 division of the Aralo-Caspian series, viz. the elevation of the latter 

 above the level of the sea. The source of such elevations in the 

 modern basin has been adverted to ; and, in the following quotation 

 from a well-known work, there is satisfactory evidence of the activity 



* Elie de Beaumont, " Extrait d'une Serie de Recherches sur quelques-unes des 

 Revolutions de la Surface du Globe," p. 45. 



t Vide D'Archiac in Mem. de la Soc. Geol. de France, 1839, vol. iii. p. 261, &c., 

 translated in Leonhard and Bronn's Jahrbuch for 1841, p. 796 ; also Bronn in 

 Jahrbuch for 1842, pp. 83, 84. 



X Dr. Fitton, op. cii., p. 290. 



