Chap. VI. MUD VOLCANOES. 77 
are formed around them. The whole place is heated in 
different degrees at various spots. 
A few miles distant, on another side of the same mountain, 
is the hervidero de Tisate. This is a small crater filled with 
a thick mud, kept in violent commotion by the steam and 
gases that escape through the boiling paste. In large 
flakes and voluminous masses the stiff mud is thrown into 
the air, and, falling down at the edge, where it quickly 
dries from the heat prevailing throughout the locality, it 
forms a circular wall of clay of an ashy colour with portions 
of various other colours similar to the clay of San Jazinto. 
In the flakes which had just fallen down while I stood near, 
and were still hot and in a pasty state, I observed in- 
numerable bright little cubes of iron pyrites, which appear 
to be continually forming in this natural laboratory. Here- 
after this paste will consolidate into a rock, with these 
cubes interspersed throughout its substance. It is not 
without scientific interest to observe this instance of the 
formation of a rock produced by the combined agency of 
fire and water, — a class of rocks and' mineral productions 
generally neglected in the speculations of exclusive geo- 
logical schools, but to which some of the rocks now called 
plutonic may one day be referred. Here and there con- 
siderable efflorescences of a white salt were seen. That it 
was a salt of iron was manifested on the spot by a cha- 
racteristic reaction. My guide, seeing that I collected a 
portion of the salt, took the fresh bark from the branch of 
a tree and rubbed its inside with the salt, by which a deep 
black colour was instantly produced. " That's the way we 
make our ink here," added the man, as a commentary on 
his chemical demonstration. 
I spent the night in a house on the hacienda de San 
Jazinto. For the hospitality which I enjoyed at this 
