OVERLYING AND WAP ROCKS. 115 



cavernous, and which are sometimes both solid and 

 cavernous, according to their depths in different places. 

 Thus may the Trap rocks have been formed among 

 the secondary strata, after their elevation, or on the 

 dry land, as well as under the sea : while the usual 

 process of waste would first remove the portions 

 peculiarly characteristic of volcanoes, or those which, 

 being superficial, are also the most cavernous. And 

 that this has actually happened in volcanic districts, 

 is indicated in Sardinia, and in many other places. 

 Thus, antient volcanoes, terrene as well as submarine, 

 may have been the origin of the present trap rocks ; 

 as is rendered further probable by their repetition in 

 the same place. Thus also might the secondary strata 

 remain covering the volcanic rock, until removed by 

 subsequent waste ; and such may be the origin of the 

 traps with flat surfaces, occupying the summits of 

 mountains; just as a future waste of the Apennines 

 would expose rocks truly volcanic, with all the cha- 

 racters of our own traps. 



This view is confirmed by the circumstances attend- 

 ing the trap rocks of Transylvania ; while the natures 

 of the substances render the argument equally appli- 

 cable to the whole tribe of these rocks. In this very 

 extensive tract tkere occur porphyries, of which some 

 almost assume the granitic character ; and it contains 

 a Solfatara, still hot, while, at Budoshegi, there are 

 also the marks of a crater. There can be no doubt 

 that these volcanic indications belong to the fires which, 

 at some remoter period, produced this tract of rock ; 

 and it is confirmed by the analogous case of the Andes, 

 where the long chain of extinct volcanoes which 

 includes Popoyan, is situated in a similar chain of the 

 same porphyries. Nothing more seems wanting to 



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