154 MAJOR IMRIE’S ACCOUNT OF GIBRALTAR. 
and bounded for the most part by rugged slopes, or by precipices; like 
other compact limestones, it is perforated by caverns of vast extent, 
and also by vertical fissures. The largest cavern (St. Michael’s) is 
1000 feet above the sea, and consists of a long series of caves, of 
difficult access, which have been penetrated to the distance of 300 
feet from the first cavern, and extend still further, and abound with 
stalactites. In this cave no bones have yet been noticed, but in the 
perpendicular fissures of the rock, and in some of die caverns (all ol 
which afford evident proofs of their former communication with the 
surface) a calcareous concretion is found of a reddish brown fer¬ 
ruginous colour, with an earthy fracture and considerable induration, 
inclosing the bones of various animals; these bones are of various 
sizes, and lie in all directions, intermixed with shells of land snails, 
fragments of the calcareous rock, and particles of spar. Bones com¬ 
bined in similar concretions are found also in Dalmatia, the islands of 
Cherso, and Ossero, and have been described by Fortis; and by his 
account it appears, that with regard to situation, composition and 
colour, they are perfectly similar to those found at Gibraltar, and occur 
in fissures and caves of the same species of limestone. I have traced 
(says Major Xmrie) in Gibraltar this concretion from the lowest part 
of a deep perpendicular fissure up to the surface of the mountain ; as 
it approached the surface, it became less firmly combined, and when 
it had no covering of the calcareous rock, a small degree of adhesion 
only remained. 
« At Rosia Bay, on the west-side of Gibraltar, this concretion is 
found in what has evidently been a cavern originally formed by huge 
unshapely masses of rock, which have tumbled in together. The 
