ANGULAR FRAGMENTS, WHY MORE ABUNDANT IN CAVES. 151 
may also have introduced the loam and pebbles through which they 
are in each case dispersed. The chief differences with regard to the 
Mediterranean breccia seem to consist, 1st. in the loam being red, 
instead of its more usual colour, brown ; an accident which may be 
explained by the hypothesis of its being diluvial detritus, derived 
from strata of a red colour, and which is rendered probable by the 
fact mentioned by Major Imrie, of there being, on the summit of the 
rock of Gibraltar, superficial deposits of a similar red earth, which 
from his description are clearly diluvial. 3d. In the proportion of 
angular fragments of stone being greater in this breccia than in that 
from the caverns: this may be referred to their having fallen in greater 
abundance from the sides of the fissures (whilst they were yet open), 
than from the roof of close caverns, in consequence of the greater 
exposure of the former to the decomposing influence of the atmo¬ 
sphere ; and this hypothesis is corroborated by the fact spoken of by 
Mr. Allan, in his excellent Paper on the Geology of Nice (Edin. 
Phil. Trans, vol. viii. part 2), that the naked surfaces of the limestone 
rocks near Nice (which are of the same kind with that of Gibraltar), 
are broken and shattered into angular fragments, which lie on the 
surface of the mountains, and are mentioned by Saussure under the 
name of « breche en place Sd. A third point wherein the breccia 
we are considering differs from that of the caverns is, that it contains 
land-shells. These may be considered as having fallen in from the 
sides of the fissures, together with the animals and the angular 
fragments last spoken of; whilst the depth and covered state of the 
» My own observation has presented to me many similar occurrences of loose naked 
angular fragments on the surface of many other compact limestone rocks. 
