PEBBLES ON THE SUMMIT OF THE BOCK OF GIBRALTAR. 157 
of the rock; it consists of pot-like holes of various sizes, hollowed out 
of the solid rock, and formed apparently by the attrition of gravel or 
pebbles, set in motion by the rapidity of rivers or currents in the sea. 
One of those which had recently been laid open I examined with at¬ 
tention, and found it to be five feet deep, and three in diameter; the 
edge of its mouth rounded off, as if by art, and its sides and bottom 
retaining a considerable degree of polish. From its mouth, for three 
and a half feet down, it was filled with a red argillaceous earth, thinly 
mixed with minute parts of transparent quartz crystals; the remaining 
foot and a half, to the bottom, contained an aggregate of water-worn 
stones, which were from the size of a goose’s egg to that of a small 
walnut, and consisted of red jaspers, yellowish white flints, white 
quartz, and bluish white agates, firmly combined by a yellowish brown 
stalactitical calcareous spar. In this breccia I could not discover any 
fragment of the mountain rock, or any other calcareous matter, ex¬ 
cept the cement with which it was combined. This pot is 940 feet 
above the level of the sea.” 
Now, comparing these facts with the phenomena he had before 
described, we see that the red earth here mentioned is the very sub¬ 
stance which, in the caves and fissures immediately below, forms the 
diluvial matrix in which the bones are embedded, and together with 
which they have been united by stalagmitic infiltrations into a mass 
of solid osseous breccia; and the pebbles of quartz, agate, jasper, &c. 
lodged with this red earth on the summit of an insulated, lofty, and 
precipitous mountain of naked limestone, present a case analogous to 
the blocks of Mont Blanc granite on the limestone mountains of the 
Jura; both being on spots from which it is impossible they could 
