AND AMERICAN RURAL SPORTS. 
225 
the transporting power of running water, to consider all the 
numerous agents which may co-operate in the lapse of ages, 
in conveying the wreck of mountains to the sea. A gra- 
nite block might remain stationary for ages, and defy the 
power of a large river; till at length a small spring may 
break out, surcharged with carbonic acid, — the rock may 
be decomposed, and a streamlet may transport the whole 
mass to the ocean. 
The subtraction of many of the elements of rocks by the 
solvent power of carbonic acid, ascending both in a gaseous 
state and mixed with spring-water in the crevices of rocks, 
must be one of the most powerful sources of those internal 
changes and re-arrangement of particles so often observed 
in strata of every age. The calcareous matter, for example, 
of shells, is often entirely removed and replaced by carbo- 
nate of iron, pyrites, or silex, or some other ingredient, such 
as mineral waters usually contain in solution. It rarely 
happens, except in limestone rocks, that the carbonic acid 
can dissolve all the constituent parts of the mass; and for 
this reason, probably, calcareous rocks are almost the only 
ones in which great caverns and long winding passages are 
found/ The grottos and subterranean passages, in certain 
lava-currents, are due to a different cause, and will be spo- 
ken of in another place. Ly ell’s Geology. 
ERUPTION OF JORULLO IN 1759. 
As another example of the stupendous scale of modern 
volcanic eruptions, we may mention that of Jorullo, in 
Mexico, in 1759. We have already described the great 
region to which this mountain belongs. The plain of Mal- 
pais forms part of an elevated plateau, between two and 
three thousand feet above the level of the sea, and is bound- 
ed by hills composed of basalt, trachyte, and volcanic tuff, 
clearly indicating that the country had previously, though 
probably at a remote period, been the theatre of igneous 
action. From the era of the discovery of the New World 
to the middle of the last century, the district had remained 
undisturbed, and the space, now the site of the volcano, 
which is thirty-six leagues distant from the nearest sea, was 
occupied by fertile fields of sugar-cane and indigo, and wa- 
tered by the two brooks Cuitimba and San Pedro. In the 
month of June, 1759, hollow sounds of an alarming nature 
were heard, and earthquakes succeeded each other for two 
months, until, in September, flames issued from the ground, 
and fragments of burning rocks were thrown to prodigious 
heights. Six volcanic cones, composed of scoriae and frag- 
mentary lava, were formed on the line of a chasm which 
ran in the direction from N.N.E. to S.S.W. The least of 
3 L 
these cones was three hundred feet in height, and Jorullo, 
the central volcano, was elevated one thousand six hundred 
feet above the level of the plain. It sent forth great streams 
of basaltic lava, containing included fragments of primitive 
rocks, and its ejections did not cease till the month of Fe- 
bruary, 1760. Humboldt visited the country twenty years 
after the occurrence, and was informed by the Indians, 
that when they returned long after the catastrophe to the 
plain, they found the ground uninhabitable from the exces- 
sive heat. When the Prussian traveller himself visited the 
locality, there appeai’ed, round the base of the cones, and 
spreading from them as from a centre over an extent of four 
square miles, a mass of matter five hundred and fifty feet in 
height, in a convex form, gradually sloping in all directions 
towards the plain. This mass was still in a heated state, 
the temperature in the fissures being sufficient to light a 
cigar at the depth of a few inches. On this convex protu- 
berance were thousands of flattish conical mounds, from six 
to nine feet high, which, as well as large fissures traversing 
the plain, acted as fumeroles, giving out clouds of sulphuric 
acid and hot aqueous vapour. The two small rivers before 
mentioned disappeared during the eruption, losing them- 
selves below the eastern extremity of the plain, and re-ap- 
pearing as hot springs at its western, limit. Humboldt 
attributed the convexity of the plain to inflation from below, 
supposing the ground, for four square miles in extent, to 
have risen up in the shape of a bladder, to the elevation of 
five hundred and fifty feet above the plain in the highest 
part. But this theory, which is entirely unsupported by 
analogy, is by no means borne out by the facts described ; 
and it is the more necessary to scrutinize closely the proofs 
relied on, because the opinion of Humboldt appears to have 
been received as if founded on direct observation, and has 
been made the groundwork of other bold and extraordinary 
theories. Mr. Scrope has suggested that the phenomena 
may be accounted for far more naturally, by supposing that 
lava flowing simultaneously from the different orifice's, and 
principally from Jorullo, united into a sort of pool or lake. 
As they were poured forth on a surface previously flat, they 
would, if their liquidity was not very great, remain thickest 
and deepest near their source, and diminish in bulk from 
thence towards the limits of the space which they covered. 
Fresh supplies were probably emitted successively during 
the course of an eruption which lasted a year, and some of 
these resting on those first emitted, might only spread to a 
small distance from the foot of the cone, where they would 
necessarily accumulate to a great height. 
The showers, also, of loose and pulverulent matter from 
the six craters, and principally from Jorullo, would be com- 
posed of heavier and more bulky particles near the cones, 
and would raise the ground at their base, where, mixing 
