1822.) 
¥ seldom could discover any well- 
defined line of separation between the 
solid and conglomerate limestones, 
though such a separation certainly 
exists. ‘The imbedded masses of the 
conglomerate, however, the nearer 
they approached the solid rock, lay 
closer together, the interstices enly be- 
tween them being filled with the 
tufaceous basis. 
That this conglomerate limestone is 
a much later formation than the inte- 
rior mass, appears from the well-known 
and interesting fact of bones and teeth 
of larze quadrapeds having been dis- 
covered imbedded in it. 
The solid limestone, from the occur- 
rence of beds of flinty slate in it, would 
appear to be a transition, or a very old 
secondary limestone, and it is ex- 
tremely improbable, that organic re- 
mains of animals, so high in the scale 
of being, should be found in it, or in 
any rock contemporaneous with it. I 
have seen some of these petrified bones 
of large animals, and they were always 
imbedded in the conglomerate rock. 
Shells also occur in it, but always 
land-shells, and similar to the commoa 
species on the hill. ‘hese shells often 
are not at all altered. Some parts of 
this conglomerate are certainly of 
later formation than other parts, and I 
haye no doubt that though slowly, its 
formation is daily going on. 
There is a considerable depth of soil 
on some parts of the hill, in particular 
near its foot. It is a red, calcareous 
kind of soil, formed in a great measure 
from the mouldering of the calc-tall; 
and appears to be very productive. 
It is highly imprebable, I think, that 
this cale-tuff basis has been deposited 
over the debris of the solid rock, from 
water which at any former period stood 
over the hill, Though I do not recol- 
Ject that springs are very numerous on 
the hill, yet I think that it is far more 
probable that this calc-tuff has been 
deposited from such springs, as is 
usual with this substance in other situ- 
ations, or from water percolating 
through the sides of the hill, and sup- 
plied, if necessary, from some great 
central reservoir, which I believe isnot 
at all an uncommon circumstance in 
limestone rocks. The calc-tuff thus 
formed, and enclosing the debris of the 
solid limestone with animal remains of 
various kinds, explain the structure 
and nature of this rock and its petrifac- 
lions, It is probable, therefore, that 
Geology of Gibraltar, 55 
petrifactions of animals of the. latest 
formation, or even of man himself, 
may be discovered in this and similar 
rocks, 
Numerous caves occur in the lime- 
stone, the sides, roofs, and floors of 
which are lined with a thick coating 
of cale-sinter, with numerous stalactites 
from the roof, aud thick, massive pil- 
lars, as usual in caves of this kind. 
Many caves formerly existed, which 
are now entirely filled with calc-sinter 
and cale-tuff. Few of these caves are 
large. St. Michael’s Cave, about 800 
feet above the level ef the sea, which 
is the largest and best known, is about 
100 feet in length, 40 in breadth, and 
40 or 50 in height. The stalactites 
are short and thick, and generally of 
a brown calc-sinter, which is heavier 
and harder than the other varieties. 
At the farther extremity of this cave 
are many deep hollows; in some of 
these I found parts of the skeletons of 
goats, which had no doubt fallen into 
these pits, and, being unable to escape, 
had there perished. Bones and skele- 
tons may in this way be often found 
in these cayes, encrusted and petrified 
by the cale-sinter. Below this upper 
cave occurs another smaller cave, but 
more beautiful, into which you de- 
scend by rope-ladders by one of these 
deep hollows. Many amusing fables 
relate to this cave. Hundreds of small 
caves occur in the rock, generally, I 
think, situate in the conglomerate, and 
filled in part with cale-sinter and calc- 
tuff. St. Michael’s Cave, however, 
occurs in the solid limestone. Some 
of these caves present most pictu- 
resque and magnificent appearanees. 
The cale-sinter of these caves, and the 
cale-tuif of the conglomerate lime- 
stone, appear to have a similar forma- 
tion; the tuff is associated with the 
sinter in the caves, the sinter is asso- 
ciated with the tuff in the rock: if the 
one, therefore, is gradually forming, 
so is the other; if the one is formed by 
percolation of wafer through the rock, 
which holds the calcareous matter in 
solution, so is the other; and thus the 
formation of the one is connected 
with, and illustrates the formation of, 
the otber. 
To the north-east of the Rock of 
Gibraltar, about fificen miles on the 
shores of the Mediterranean, rises a 
very lofty range, called the Alpuxara 
Mountains, steep, massive, and bare, 
f did not examine these hills, but they 
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