iSlew Observations on Volcanoes and their Lavas. 223 



The academicians measured in this high region three de- 

 grees of the meridian, from Cuen9a on the south to the 

 equinoctial line to the north of Quito, not far from the grand 

 volcano of Cayambairo. This valley being bordered on both, 

 sides, through all its length, with very high volcanoes, its 

 soil must be composed entirely of an accumulation of the 

 substances they have vomited ; they have heaped vip the 

 space which originally separated the two lines of volcanoes, 

 and raised the valley to its present height. It is not asto- 

 nishing that M. Humboldt did not find any slate, micaceous 

 scbistus, gneiss, or any vestige of granite; but what is particu- 

 larly astonishing is, as he says, that granite always occupies 

 the highest parts of the globe in the temperate zones. It is 

 nof, therefore, at all ascertained that in this part of the Cor- 

 delier, every thing being tlie work of subterraneous fires, 

 there is any bed of natural rocks. This is probably the reason 

 why he had recourse to porphyry, from the porphyroidal 

 appearance of several lavas. Such are the errors into which 

 we may fall, when we adopt the Neptunian system, in mis- 

 taking the productions of fire. 



Beyond the two lines of volcanoes their sides are joined 

 by the s\iccessive extension of their bases, and show a suci-- 

 cession of heaps of the same matter : this is pointed out in 

 a very precise manner by the observations cf the academi- 

 cian. These exterior shelves being very old, and descend- 

 ing into the region of vegetation, they are covered with herbs 

 and forests wherever the torrents have not torn up ravines. 

 The base of Mount ^tna is also covered with forests, and 

 that of Vesuvius with gardens and vineyards, which are often 

 destroyed by new eruptions. Perhaps one of the layers 

 through which the volcano of the Cordelier shows itself 

 appears at the exterior : their numerous eruptions may have 

 covered them. The foot of the cones which rise from the 

 valley ought not to be considered as the base of the volcano. 

 Their base is at the level of the sea, and the focus of the 

 crater is considerably below it. 



Bouguer, but slightly acquainted with volcanoes and vol- 

 canic matters, saw only, in the different beds of the lavas 

 and scoriae of Cotopaxi, stones simply burned of various co- 



Vol. 27. No. 107. April 1807. i* lours; 



