THE ROYAL ARTILLERY INSTITUTION. 
SO] 
covered by a gunner of tbe Royal Artillery, some years ago; it is about 
600 ft. above the sea level, although becoming daily less, as from constant 
observation, we know that the Rock is gradually sinking, and at 
Gibraltar some future period the eye-sore of Spain, and oft bone of 
8m mg ‘ contention of Europe, may disappear beneath the sea, as it has 
been known to have done before by many geological proofs, and the 
nautical charts of future generations may mark its place only as a dangerous 
shoal or reef. 
At the height of this cave and some 50 ft. above may be seen the celebrated 
minute shell breccia before mentioned (see specimen No. 4), and near here 
is a waterworn conglomerate of some extent, manifestly at one time a sea 
beach, thus affording another proof of the force of upheaval the Rock has 
undergone. 
On the north side of the Rock is Poca Roca cave; in excavating 
Cave R ° Ca an ^ blasting the rock, near this cave late in 1864, to obtain a 
suitable ground for a small gun park, a large fissure was found, 
filled up with bone breccia, the bones being various, but chiefly of small 
animals, such as ibex, rat, deer, &c., &c. much the same as those found some 
years before near the galleries, hardly any being so ancient as those of 
“ Genista Cave " or so important, from this fissure (specimens No. 8 of 
minute bone breccia, No. 12 of land shell breccia, and No. 20 of a deer's 
tooth) are taken; this cave seems to have been formed by the violent 
concussion that rent “ the Rock " mid-way between the signal station and 
rock gun battery, near to Middle Hill, evident marks of the disturbance 
being found. 
Now lastly turning to the long celebrated, and far-famed cave 
Cave 1Claael,S ^ Michael, we find traces of the disturbance extending from 
the south side of the signal station, through St Michael's Cave, 
passing a small cave near the “ Old Man's Garden," down to Windmill Hill, 
the Genista Cave being probably formed by the same violent force of 
upheaval, as the axes of fracture of all three are nearly identically in a line; 
wishing to know if this celebrated cave, which consists of a long fissure, 
could afford us any further information on the bone breccia 
Michaers S Cave 9 ues ti 0I b and also wishing to solve certain doubts, and the truth 
between tbe of certain rumours respecting this cave, I determined upon a 
Sid jitoe f, 66 >r ’ care ^ exploration, with such instruments as I deemed requisite 
for the purpose. 
On the 2lst April accompanied by Capt. Jerome, and Dr Jackson of the 
86th Regiment, and Serjt. T. Hanson, and Bomb. R. Smith of the Royal 
Artillery, &c. the first exploration was made. On arriving at the “Grotto" 
the difficulties and labours became so great, that my party which had been 
gradually thinning, now consisted, besides myself, of Serjt. Hanson and 
Bomb. Smith, to these two intelligent n.-c. officers who assisted me from 
time to time in most of my subsequent explorations, and scientific inves¬ 
tigations in this cavern, much of the success which attended our labours is 
due; we found the depth, from the entrance of the cavern (which is about 
937 ft. above the sea level), to the floor of the “ Grotto " (the lowest part) 
to be 265 ft., and to the “ Prison" 245 ft., the greatest depth also to the 
spot now known as “ Hanson's Cave " to be 257 ft., while that of “ Brown's 
Seat" at the extreme end was somewhat less being 242 ft., the distance of 
