92 



or that the porous rock lay on compact strata, as 

 happens in the currents of lava of .'Etna and 

 Vesuvius. The marl *, which alternates more 

 than a hundred times with the basalts, is yellow- 

 ish, friable by decomposition, very coherent in the 

 inside, and often divided into irregular prisms, 

 analogous to the basaltic prisms. The sun dis- 

 colours their surface, as it whitens several schists, 

 by reviving a hydrocarburetted principle, which 

 appears to be combined with the earth. The marl 

 of Graciosa contains a great quantity of chalk, 

 and strongly effervesces with nitric acid, even on 

 points where it is found in contact with the ba- 

 salt. This fact is so much more remarkable, as 

 this substance does not fill the fissures of the 

 rock, but it's strata are parallel to those of the 

 basalt ; whence we may conclude, that both fos- 

 sils are of the same formation, and have a com- 

 mon origin. The phenomenon of a basaltic rock 

 containing masses of indurated marl split into 

 small columns, is also found in the Mittelgebirge, 

 in Bohemia. Visiting those countries in 1792, 

 in company with Mr. Freiesleben -jf, we even re- 

 cognized in the marl of the Stiefelberg the imprint 

 of a plant nearly resembling the cerastium, or the 

 alsine. Are these strata, contained in the trap- 

 pean mountains, owing to muddy irruptions ? or 

 must we consider them as sediments of water, 



* Mergel. 



I Berginaennisches Journal, 1792, p. 2i5. 



