304 On the relative Age of the 



lion lias elevated in our times, above their original level ? The 

 reply to these questions must be aflirmalive, of which we have 

 the following proof furnished by M. dc Humboldt. 



In the night of the 28th and 29th September 1759, a piece 

 of ground three or four miles square, situated in the intendancy 

 of Valladolid, in Mexico, rose in the form of a bladder. The 

 limits at which the raising was stopped, are still recognized by 

 the fractured strata. At these limits, the elevation of the ground 

 above its original level, or rather above that of the surrounding 

 plain, is only 37 feet ; but towards the centre of the upraised 

 space, the total raising has not been less than 500 feet. 



This phenomenon was preceded by earthquakes, which lasted 

 nearly two months ; but when the catastrophe happened, every 

 thing seemed quiet, and it was only announced by a horrible 

 subterranean noise which took place at the moment when the 

 ground rose. Thousands of small cones from two to three yards 

 high, and which the natives call hornitos, issued in all parts. 

 At length, in the direction of a long crack running from north- 

 north-east to south-south-west, there suddenly arose six large 

 masses, all of them elevated from four to five hundred yards 

 above the plain. The largest of these six hills is a true volcano 

 (the volcano of Jorullo), vomiting basaltic lavas. 



We thus see that the most evident and the most distinctly cha- 

 racterized volcanic phenomena accompanied the catastrophe of 

 Jorullo, and that they have probably been the cause of it ; but 

 all this says nothing against the fact that an extensive, ancient, 

 and perfectly consolidated plain, in which sugar-cane and indigo 

 were cultivated, has been in our time suddenly transported to a, 

 great height above its original level. The eruption of burning 

 matter, and the formation of the hornitos, and of the volcano of 

 Joiiillo, so far from having contributed to produce this effect, 

 must on the contrary have lessened it ; for all these apertures 

 acting as safety-valves, would have allowed the elevating cause 

 to disperse, whether it was gas or vapour. If the ground had 

 opposed more leslstance, if it had not yielded ni so many points, 

 the plain of Jorullo, in place of becoming a mere hill 500 

 feet high, might have acquired the elevation of any neigh- 

 bouring simimit of the Cordilleras. 



The circumstances which accompanied the formation of a new 



