*
[footnote] (Humboldt, 'Geognost. Beobach, uber die Vulkane des Hochlandes
von Quito', in Poggend., 'Annal. der Physik', bd. xliv., s. 194.
The focus of the volcanic action lies below the whole of the highlands of
this province; the only channels of communication with the atmosphere are,
however, those mountains which we designate by special names, as the
mountains of Pichincha, Cotopaxi, and Tunguragua, and which, from their
grouping, elevation, and form, constitute the grandest and most picturesque
spectacle to be found in any volcanic district of an equally limited extent.
Experience shows us, in many instances, that the extremities of such groups
of volcanic chains are connected together by subterranean communications;
and this fact reminds us of the ancient and true expression made use of by
Seneca,* that the igneous mountain is only the issue of the more
deeply-seated volcanic forces.
[footnote] *Seneca, while he speaks very clearly regarding the
problematical sinking of Aetna, says in his 79th letter, "Though this might
happen, not because the mountain's height is lowered, but because the fires
are weakened, and do not blaze out with their former vehemence; and for
which reason it is that such vast clouds of smoke are not seen in the
day-time.
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