GEOLOGY. 311 



phur the holes and interstices between the fragments of rock of which the 

 cone is composed. 



We failed, in the expedition of 1845, to study the volcanic and vegetable 

 products which the crater presented. In order to examine its actual state;, 

 and to fill this blank, I descended on the 16th of December, 1857, carrying, as 

 far as possible, what was necessary for the perilous situations in which I 

 expected to be placed. I was engaged little more than three hours in the 

 descent, and half-past eleven of the day found me at the cone of eruption. 

 The form which this presents proves that the bottom of Pichincha has been 

 recently the theatre of considerable convulsions. The vegetation which cov- 

 ered it has disappeared from the eastern side ; the depression which exists 

 towards the southeast, at the foot of the cone, has widened itself, and lias 

 filled up a part of the broken enclosure, interrupting it perpendicularly with 

 a broad wall of stones, undoubtedly shot out from its interior. Near to this, 

 and towards the south, it has formed, since 1845, a new depression, or, speak- 

 ing more properly, a new accidental crater, from whence arises a great mass 

 of vapor, so that the cone of eruption has at present three apertures or 

 craters: the principal occupying the higher part: the ancient accidental 

 crater placed at the southeast and at the foot of the former; and the new 

 accidental crater open likewise at the foot and at the south of the principal 

 one. 



The volcanic activity of Pichincha has increased remarkably, as is mani- 

 fested by the greater exhalation of vapors. In 1845, the chimneys from 

 Avhence the gases arose formed six groups, of which only one was consider- 

 able. Now the vapors escape by innumerable interstices and hollows which 

 the stones leave in each of the craters; and in the principal one is heard a 

 noise resembling that made by an immense caldron of boiling water. 



The temperature of the vapors varies much in the different interstices. In 

 the crater of the southeast, the vapors of the highest interstices are nearly 

 188.0 Fahrenheit, whilst in the lower ones the temperature was only 140 

 Fahrenheit. In the principal crater, the hottest vapors did not come up to 

 194 Fahrenheit ; in the largest interstice that I have observed, into which a 

 person could easily enter, if the thick column of vapor would permit him, 

 the temperature was only 98.6 Fahrenheit at three feet of depth. Filling a 

 graduated tube with water, and placing it within the interstices, I collected 

 the gases several times in order to analyze them, and, moreover, condensed 

 them, by means of a bottle filled with cold water, and gathered the drops of 

 fluid which were formed. The result of my observations is, that the gases of 

 Pichincha contain a scarcely perceptible trace of sulphurous, sulphuric, and 

 sulphydric acids, four per cent of carbonic acid, and the rest composed exclu- 

 sively of water. I present these results only as approximate ones. The 

 atmospheric air is always mixed with the volcanic gases in those points 

 where it is possible to collect it; and this cause of error is inevitable, with- 

 out reckoning those which occur from the personal difficulties of the observer. 



The solid products of the volcano are the sublimed sulphur which covers 

 almost all the stones and fissures, and a white salt which appears in silky 

 fibres, and shows itself in many of the interstices, sometimes alternating 

 with the flour of sulphur in parallel coatings, sometimes in. an abundant 

 and pure mass. This salt is a double sulphate of alum and of the protoxide 

 of iron, likewise formed in other volcanoes, and known by the name of 

 " alumbre de pluma," or plumose alum. Dissolved in Avater, it crystallizes by 

 spontaneous evaporation in a derivative form of the oblique rhomboidal 



