INTERIOR OF THE CRATER. 
75 
She top of these volcanoes, nothing obstructs tlio view of the 
bottom of the crater. The peaks of Teneriffe anil Cotopaxi, 
on the contrary, are of very different construction. At their 
summit a circular wall surrounds the crater; which wall, at 
a distance, has the appearance of a small cylinder placed on 
R truncated cone. On Cotopaxi this peculiar construction 
is visible to t he naked eye at more than 2,000 toises distance ; 
and no person has ever reached the crater of that volcano. 
On the peak of Teneriffe, the wall, which surrounds the 
crater like a parapet, is so high, that it would be impossible 
to reach the Caldera, if, on the eastern side, there was not a 
breach, which seems to have been the effect of a flowing of 
very old lava. W'e descended through this breach toward 
the bottom of the funnel, the figure of which is elliptic. Its 
greater axis has a direction from north-west to south-east, 
nearly ]S T . 3o J W. The greatest breadth of the mouth 
appeared to us to be 300 feet, the smallest 200 feet, which 
numbers agree very nearly with the measurement of MM. 
V erguin, Varela, and Borda. 
It is easy to conceive, that the size of a crater does not 
depend solely on the height and mass of the mountain, of 
which it forms tiio'pnueipal air- vent. This opening is indeed 
seldom in direct ratio with the intensity of the volcanic lire, 
or with the activity ot the volcano. At Vesuvius, ■which is 
but a bill compared with the Peak of Tenerilt'e, the diameter 
of the crater is five times greater. When we reflect, that 
very lofty volcanoes throw out less matter from their summits 
thau from lateral openings, we should be led to think, that 
the lower the volcanoes, their force and activity being the 
same, the more considerable ought to be their craters. In 
fact, there are immense volcanoes in the Andes, which have 
but very small openings; and we might establish as a 
geological principle, that the most colossal mountains have 
craters ot little extent at the summits, if the Cordilleras did 
not present many instances to the contrary * I shall have 
occasion, in the progress of this work, to cite a number of 
tacts, which will throw some light on what maybe called the 
external structure ot volcanoes. This structure is as varied 
* 1 he great volcanoes of Cotopaxi anti Rucupiehincha have craters, the 
diameters of which, according to my measurements, exceed 400 and 70C 
to'ses. 
