649 



felt even in our mines of the least depth, and 

 which since Heraclitus of Ephesus, and Anax- 

 agoras of Clazomane, to the Plutonism of mo- 

 dern times, has been considered as the seat of 

 the great agitations of the globe. 



The sketch I have just traced furnishes all the 

 formations we know in that part of Europe, 

 which has served as the type of positive geog- 

 nosy. It is the fruit of a labour of sixteen 

 months, often interrupted by other occupations. 

 The formations of quartziferous porphyry, py- 

 roxenic porphyry and trachyte, of grauwacke, 

 muschelkalk, and quadersandstein, which are 

 frequent towards the west, have not yet been 

 recognized in Venezuela ; but it may be also 

 observed that, in the system of secondary rocks 

 of the antient continent, muschelkalk and 

 quadersandstein are not always clearly deve- 

 loped, and are often by the frequency of their 

 marls, confounded with the lower shelves of 

 jurassic limestone. The muschelkalk is almost 

 a lias* with encrinite, and quadersandstone (for 

 there are doubtless many above the lias or 

 limestones with gryphites) seems to me to re- 

 present the arenacious layers of the lower 

 shelves of jurassic limestone. I thought it my 

 duty to give an extensive developement to the 



- 



* See the judicious reflexions of M. Boue, in his Memoir 

 on the Alps, p. 24. 



