Torrents of Hot Water, Air Volcanoes and Cold Springs. 311 
ish substance, (calc-tufF, sinter and travertine ?), which ac- 
quires a great degree of hardness. The spring- water is so highly- 
impregnated with the earthy matter, that the inhabitants receive 
it in square boxes or moulds, which it fills in a few days, and the 
blocks, thus formed, are used for building. Indeed the greater 
part of Guancavelica, like Rome, is built of the concretionary 
rock formed from springs 
% RocTas formed from torrents of Hot-Water issuing from VoU, 
canoes. 
There are on record authentic instances of torrents of hot 
water flowing from the crater or the sides of volcanoes, when in 
a state of activity, which, when collected in hollows, or spread 
over plains, deposites various earthy matters, which at length 
assume the character of rocks. In the year 1751, a torrent of 
salt water burst from ^tna, and continued lo flow for a quarter 
of an hour, and was so considerable that the inhabitants named 
it Nilo d'Acqua. Dolomieu and Hamilton observed traces of a 
frightful torrent of hot water which had issued from the great 
crater of ^tna ; and Spallanzani is of opinion, that part of the 
tuffas of Italy have been formed by muddy eruptions. In 
those volcanic mountains whose summits are above the snow 
line, as is the case in Iceland and in South America, great floods 
of hot water, charged with earthy matter, burst from the moun- 
tains and devastate the surrounding country. Bouguer and 
Condamine saw dreadful ravages committed by these torrents; 
and the latter writer informs us, that after an explosion of Coto- 
paxi, a village' situated thirty leagues in a straight line, and pro- 
bably sixty leagues following the wavings of the ground, was en- 
tirely carried away by one of those torrents. These torrents from 
the ice-caped volcanoes, appear to be entirely external, while those 
first mentioned seem to come from the interior of the volcanoes. 
• Masses of siliceous matter, probably the formation of hot-springs, have been 
found, inclosing foreign bodies of different kinds. Of this description are the 
masses of siliceous matter inclosing coins, described by authors, and which have 
been held as fabulous. The following is an instance of this fact. In the year 1812, 
a mass of flinty matter, twelve inches long, was dug up in France, in the interior 
of which there were several coins, the most ancient of which were of the sixteenth 
century. {Journal des MineSf p. 23.) Vegetables are also occasionally found 
included in a siliceous basis of an opaline or chalcedonic nature, and of these 
Daubenton and others have given particular descriptions. 
