530 A. C. RAMSAY AND J. GEIKIE ON 



in other places the accumulations are quite soft and incoherent. 

 Stones falling from the cliffs above would plunge into the unconso- 

 lidated sand, and become drifted over and buried; while the frag- 

 ments that alighted upon the hardened sand would remain in that 

 position uncovered. Such would appear to have taken place with 

 the calcareous sandstones in the neighbourhood of Monkey's-Cave 

 Eoad. The blocks which they contain in their upper portions are 

 quite angular, and these were probably dropped upon the yielding 

 parts of the sand-slope and gradually drifted up ; while in other places, 

 where the sandstone contains no blocks, but is covered directly by 

 agglomerate, we may reasonably infer that the sand had already 

 become hardened by infiltration before the stones began to fall upon 

 its surface. The general structure of the deposits at and near Mon- 

 key's-Cave Eoad is shown in the accompanying section (fig. 12). 



From the evidence now adduced there can be no doubt that the 

 limestone-agglomerates of Gibraltar belong to at least two distinct 

 stages, the older accumulations being separated from the later masses 

 by a considerable period of time. The Buena-Yista agglomerate was 

 formed long anterior to the depression of the promontory, and under 

 somewhat severe conditions of climate. The later agglomerates, on 

 the other hand, overlie and obscure the terraces of marine erosion 

 and the banks and beds of calcareous sandstone which rest upon 

 these. The younger limestone-agglomerates, like the older accumu- 

 lations, owe their origin to cold climatic conditions, although these 

 were probably not so severe as during the earlier stage. The bone- 

 breccias, again, indicate a connexion between the two continents of 

 Europe and Africa, under mild and genial conditions of climate, 

 while the calcareous sandstones show that these genial conditions 

 continued during the period of depression. 



Pkobable Succession of Events during Accumulation of 

 Superficial Deposits. 



The oldest of all the superficial accumulations of Gibraltar is 

 undoubtedly the great limestone -agglomerate of Buena Vista and 

 that neighbourhood. As it rests directly upon the truncated edges 

 of the Secondary rocks, there is no evidence as to the geographical 

 and climatic conditions that obtained before it began to accumulate. 

 We have seen that this remarkable deposit implies the former preva- 

 lence of an extreme wintry climate, and this is still further shown 

 by the fact that no fossil remains of any kind whatever have been 

 detected in it. We searched narrowly the many exposures of 

 the rock in question, but failed to meet with a trace of any thing 

 organic ; and Mr. Roberts assured us that the only fossils that were 

 ever found within the area occupied by it occurred in fissures of 

 precisely the same character as those that traverse the solid lime- 

 stone. The best known of these fissures is that of Eosia Bay. It 

 is seen cutting across the limestone- agglomerate in a vertical direc- 

 tion, and is therefore indubitably of more recent date. Enormous 

 quantities of bones were obtained from this fissure during the opera- 



