Ch. XXL] NAME OF " GRYPHITE LIMESTONE.' 1 41 7 



to account even for such partial breaks as have been alluded to in the 

 succession of species, if we reject the hypothesis that the old species 

 were in each case destroyed at the close of the deposition of the 

 rocks containing them, and replaced by the creation of new forms 

 when the succeeding formation began. I agree with Professor Earn- 

 say in not accepting this hypothesis. jSTo doubt some of the old 

 species occasionally died out, and left no representatives in Europe or 

 elsewhere ; others were locally exterminated in the struggle for life 

 by species, which invaded their ancient domain, or by varieties better 

 fitted for a new state of things. Pauses also of vast duration may 

 have occurred in the deposition of strata, allowing time for the modi- 

 fication of organic life throughout the globe, slowly brought about by 

 variation as well as by extinction. 



In some parts of France, near the Yosges Mountains, and in Lux- 

 embourg, M. E. de Beaumont has shown that the lias containing 

 Gnjphcea arcuata, Plagiostoma giganteum (see fig. 437), and other 

 characteristic fossils, becomes arenaceous ; and around the Hartz, in 

 Westphalia and Bavaria, the inferior parts of the lias are sandy, and 

 sometimes afford a building-stone. 



The name of Gryphite limestone has sometimes been applied to 

 the lias, in consequence of the great number of shells which it con- 

 tains of a species of oyster, or Gryphcea (fig. 438, see also fig. 387, 

 p. 395). A large heavy shell called Hippopodium (fig. 439), allied to 



Fig. 437. 



Fisc. 43S. 



Gryphcea incicrva, Sow. 



(G. arcuata, Lam.) 



Lias. 



Plagiostoma (Lima) giganteum, Sow. 

 Inf. Ool. and Lias. 



Cypricardia, is also characteristic of the lower lias shales. The Lias 

 formation is also remarkable for being the newest of the secondary 

 rocks in which brachiopoda of the genera Spirifer and Leptcena (figs. 

 440, 441) occur : no less than nine species of Spirifers are enumer- 

 ated by Mr. Davidson as belonging to the Lias. These pallio- 

 branchiate mollusca predominate greatly in strata older than the 

 Trias ; but, so far as we yet know, they did not survive the Liassic 

 epoch. The marine beds of the Lias also abound in cephalopoda 

 27 



