INTERGLACIAL EPOCHS. 325 



self to the action of severe frost, which broke up the rock and 

 permitted the debris to be carried down the slopes and over 

 the low ground by n6vi and melting snow and rain. We found 

 that the formation of this remarkable breccia took place at two 

 distinct periods, separated from each other by a long period of 

 milder conditions. The accumulation of the breccia of the first 

 cold epoch had ceased, and the loose agglomeration of grit and 

 large and small blocks had become cemented into an indurated 

 mass long before the formation of the later breccias was effected. 

 Torrents had worn gullies in the older breccia, and acidulated 

 water percolating through crannies and fissures had gradually 

 opened out a series of subterranean galleries and caves, which 

 penetrated the mass in the same manner as they traversed the 

 limestone-strata. All this took place at a time when Spain 

 projected farther into the Mediterranean than it does now, and 

 when the climate was mild and genial. At the period referred 

 to Gibraltar must have appeared as a verdure-clad alp, towering 

 above the surface of a wide expanse of undulating country that 

 stretched south towards the coasts of Barbary, with which, 

 indeed, it may actually have been connected. The Kock was 

 then tenanted by the ibex in great numbers, and visited from 

 time to time by rhinoceros, elephant, horse, boar, and deer, and by 

 bears, wolves, hysenas, lions, leopards, lynxes, and servals, some 

 of which may have made their lair in one or other of its numerous 



Pliocenic strata which were ploughed into by the Pleistocene glacier, and 

 re-arranged by water escaping from it. Having gone over the sections myself in 

 1878, and examined the disputed points, I came to the same conclusion as 

 MM. Riitimeyer and Mayer. The phenomena are merely a repetition of similar 

 appearances in the glacial deposits of our own islands and Northern Germany, 

 where in the boulder-clay and its associated glacial sand and gravel, we occa- 

 sionally detect the shells of marine and freshwater molluscs, together with 

 fragments of wood, bone, etc., — the relics of some pre-existing interglacial strata, 

 which the glacial forces have broken up and commingled with other dibris. 

 M. Falsan had already (1875) suggested this explanation of the phenomena from 

 from having observed in the neighbourhood of Lyons that the Pliocene contains 

 many fossils derived from the Miocene, and that the basement - part of the 

 Pleistocene glacial deposits (morainic detritus of the ancient Rhone glacier) shows 

 a similar commingling of derivative shells perfectly well preserved and mixed 

 pell-mell with boulders and striated stones ; see Bull. Soc. Giol. France, 3 e Ser. 

 t. iii. p. 727. 



