226 
THE CABINET OF NATURAL HISTORY 
with rain, they might have given rise to the stratum of 
black clay which is described as covering the lava. The 
small conical mounds (called “hornitos” or ovens) may 
resemble those five or six small hillocks which existed in 
1823, on the Yesuvian lava, and sent forth columns of va- 
pour, having been produced by the disengagement of elastic 
fluids heaving up small dome-shaped masses of lava. The 
fissures mentioned by Humboldt as of frequent occurrence, 
are such as might naturally accompany the consolidation of 
a thick bed of lava, contracting as it congeals; and the 
disappearance of rivers is the usual result of the occupation 
of the lower part of a valley or plain by lava, of which there 
are many beautiful examples in the old lava-currents of 
Auvergne. The heat of the “hornitos” is stated to have 
diminished from the first, and Mr. Bullock, who visited 
the spot many years after Humboldt, found the temperature 
of the hot spring very low, a fact which seems clearly to 
indicate the gradual congelation of a subjacent bed of lava, 
which, from its immense thickness, may have been enabled 
to retain its heat for half a century. 
Another argument adduced in support of the theory of 
inflation from below, was the hollow sound made by the steps 
of a horse upon the plain, which, however, proves nothing 
more than that the ^materials of which the convex mass is 
composed are light and porous. The sound called “ rim- 
bombo” by the Italians, is very commonly returned by 
made ground , when struck sharply, and has been observed 
not only on the sides of Vesuvius and other volcanic cones 
where there is a cavity below, but in plains such as the 
Campagna di Roma, composed in great measure of tuff and 
porous volcanic rocks. The reverberation, however, may, 
perhaps, be assisted by grottos and caverns, for these may 
be as numerous in the lavas of Jorullo, as in many of those 
of iEtna: but their existence would lend no countenance to 
the hypothesis of a great arched cavity, or bubble, four 
square miles in extent, and in the centre five hundred and 
fifty feet high. A subsequent eruption of Jorullo happened 
in 1S19, accompanied by an earthquake; but unfortunately 
no European travellers have since visited the spot, and 
the only facts hitherto known are that ashes fell at the 
city of Guanaxuato, which is distant about one hundred and 
forty English miles from Jorullo, in such quantities as to 
lie six inches deep in the streets, and the tower of the cathe- 
dral of Guadalaxara was thrown down. Lyell. 
BLACK GROUSE. 
The Black Grouse, black game , or black cock, ( tetrao 
tetrix,') though inferior in size to the cock of the woods, is 
still a bird of considerable dimensions, being much larger 
than the red grouse; and when full-grown, larger than the 
pheasant. The black cock is a very handsome bird; the 
general colour is black, but it is irridescent, and in certain 
positions of the light shows a very fine purple. The tail is 
very much forked, the outside feathers curled, and the 
lower part, towards the base, white. Upon the throat there 
is a kind of down, but no long or regularly-formed feathers. 
The length of the male bird is about twenty-eight inches, 
and the extent of the wings nearly three feet; and the weight 
between three and four pounds. The female is a much 
smaller bird, and has not the curled feathers in the tail. 
Though the places at which the Black Grouse is found are 
not quite so elevated — so near to the summits of the moun- 
tains as the habitations of the ptarmigan — it is a bird fond of 
wild and secluded spots; and its numbers in these islands 
are very fast declining. What with improvements of land, 
and improvements in the arts of its destruction, it is not 
nearly so abundant in England as it was formerly; though 
it be still met with in the more elevated and secluded places 
in the south of England, in Staffordshire, in North Wales, 
and generally where there are high and lonely moors. In 
the Alpine parts of Scotland it is more abundant, though 
the introduction of sheep, generally, upon the mountains, 
is said to be diminishing the numbers. The black cocks 
are more frequently found in the woods than the red grouse, 
though the moors, with a difference of elevation, be the 
favorite abodes of both. Their food is also similar; consist- 
ing of mountain-berries, the tops of heath, and the buds of 
pine and other Alpine trees. Though they seek their food 
in the open places during the day, they, where they have 
the accommodation of trees, perch during the night like 
pheasants. It is chiefly during the winter months, how- 
ever, and the early parts of spring, when all food, save the 
tops of the pines, is hidden under the snow, that they do 
that; for when the breeding season commences, they assem- 
ble on the tops of the mountains and highest parts of the 
moors, but never higher than they can find heath; the young 
shoots and embryo blossoms of which are at that time their 
principal food. 
Some parts of their character resemhle that of common 
poultry. They do not pair; but when the breeding season 
commences, the cocks ascend to the tops of the mountains, 
and clap their wings and crow; to which call the females an- 
swer, by making their appearance, and uttering a sort of 
clucking sound. War immediately ensues among the 
males, as each is anxious to have in his train as many 
females as possible. Their heels are armed with spurs: 
Iheir mode of fighting is the same as that of game-cocks, 
and they enter upon the strife with the same devotedness. 
Although upon other occasions they are among the shyest of 
