Natural History of Volcanos and Earthquakes. 49 
mountain has sunk in consequence of a subterranean shock 
which took place before the discovery of America. At the pres- 
ent time Capac-Urcu is lower than Chimborazo. Boussingault 
alludes to many instances, in which it is asserted, that the Cor- 
dilleras have sunk. Without taking into consideration the infer- 
ences drawn from barometrical measurements, made by Bous- 
singault and his predecessors, which seem indeed to confirm that 
supposition, we will only mention the following circumstances. 
The French academicians, who, a century ago, were sent to 
Quito for the purpose of determining the form of the globe, were 
very much embarassed in their station on Guaguapichincha, by 
the snow surrounding their signals. Now, for many years, no 
snow has been found on the summit of this mountain. The in- 
habitants of Popayan have also remarked, that the inferior limit 
of the snow covering the Purace is gradually rising, whilst the 
Inean temperature has remained the same for the last thirty 
years, whence Boussingault infers, that the Purace is sinking 
down. 
That masses thrown up in a state of igneous fusion sink again 
by degrees, in consequence of their consolidation and contraction, 
cannot be doubted. But even if their elevation had taken place 
in a solid state, yet the immense masses of the Andes have risen 
from depths, where a pretty high temperature prevails. Suppos- 
ing the Andes to have risen 24,000 feet in height, that part of 
them which is now at the level of the sea, must have been be- 
fore the elevation so many thousand feet below it. This part 
brought, therefore, with itself from beneath, a temperature which 
Was ‘4°00 —470° F. higher than that which existed at the level 
of the sea before the elevation. ‘The same holds good of each 
Patt of the Andes, in any depths, so that every where in erupted 
Masses the temperature surpassed that of the adjacent rocks by 
470° F. Whilst now these masses gradually lost their surplus 
of heat, they were contracted. But this cooling of these masses 
©an, as far as they are within the earth, only be affected by con- 
duction, therefore a long period will elapse for that purpose. 
That part of the Andes, which is elevated above the surface of 
the earth, and is exposed to the atmosphere, will of course cool 
@ little more quickly. If the bases of the rocks thrown up be at 
# great depth below the surface, their contraction in consequence 
of their cooling may be very considerable, and as the elevation 
Vol. *xxvu, No. 1.—July, 1839, bis. 7 
Mo, BOT. GARDEN 
~~ 4910 : 
