GEOLOGY OF PART OF CUBA. Q11 
We have sufficiently adverted to the extensive changes of position and inclination, and 
the striking modifications visible in the composition of almost every rock we have seen 
on this quarter of the island. ‘Towards the western part of Cuba, this influence, among 
many other manifestations, is seen in the injection of liquid petroleum and mineral pitch, 
not only in the form of veins in the old stratified rocks, but in filling cells within the 
chalcedony and quartz veins by which those rocks are traversed. In the intermediate 
area under consideration this modifying influence is displayed in the partial vitrifaction 
of the serpentine and allied rocks;—in the opalized condition of the materials at the out- 
crops of its mineral veins;—in the admixture and close proximity of undoubted igneous 
rocks ;—in the conversion of quartz into a species of porcelain ;—in the kneading together 
of the horizontal strata and lamine, into contorted and fantastic forms in some cases;—in 
the complete obliteration of these original planes of stratification in others;—in the de- 
struction, with a few exceptions, of all traces of organic forms; and in its conversion from 
a stratified state to that of a compact mass. 
THE LIMESTONE MOUNTAIN OF LA SILLA—OR THE SADDLE. 
We shall now proceed with a few details of this remarkable mountain, and, in so doing, 
our description will not be greatly inapplicable to several others in this first or northern 
chain. We have only approached it from the north and west, where it presents a preci- 
pitous escarpment, whose summit, like that of the Cerro Colorado, or Red Mountain, is 
attainable only at one or two points. The barometer being injured in the ascent, no 
admeastrements of altitude, to be relied upon, in the emergency, were undertaken. The 
principal crest was found to be a sharp ridge; a mere wall of pointed rocks, which 
descended vertically on both sides. Here then was the keystone, as it were, of that great 
anticlinal arch, which stretches far away ina W. 8S. W. direction and its reverse. From 
its upheaved centre declined the vast series, the innumerable varieties of rocks, at a high 
angle, northward towards the sea and southward towards the mineral savanas of the 
interior, which we shall hereafter describe. 
THE CAVES OF LA SILLA. 
The Gibara rock, apparently the same as has acquired in Western Cuba, and in Ja- 
maica, the name of cavernous limestone, presents, within the mountain of La Silla, some 
examples of these caverns well worthy of our notice. At the foot of a perpendicular cliff 
is the entrance to the caves of La Silla. ‘They branch to the right and to the left, so as 
to form suites of chambers, one beyond the other. The suite which lies on the west or 
left hand side of the main entrance or vestibule, is three hundred and fifty feet long. Into 
the eastern range we did not penetrate, on account of the contraction of the entrance, even 
within a very few years, by the accumulation of recent carbonate of lime upon the walls; 
or by what is not unaptly termed “growing up.” ‘The interior of the first bears a rude 
resemblance to an ancient Saxon Crypt, with its heavily groined roof and its massy pil- 
tars and buttresses, composed of continually augmenting stalactitical matter. ‘This con- 
