THE GEOLOGY OE GIBRALTAR. 539 



sonable to conclude that the former cold conditions to which the 

 Gibraltar limestone -agglomerates testify could not have been due 

 either to an elevation of the Mediterranean area, or to a submergence 

 of the Sahara, or to both of these combined. We appear, therefore, 

 shut up to the belief, as the most probable explanation of the phe- 

 nomena described in this paper, that the cold conditions referred to 

 were contemporaneous with that general refrigeration which took 

 place over so vast an area in our hemisphere during the Pleistocene 

 or Quaternary period. When we remember that large glaciers 

 existed then, not only in the Sierra Nevada, but in the Atlas, the 

 Lebanon, and in Anatolia, while at the same time the glaciers of the 

 Caucasus and the Alps greatly exceeded their present dimensions, 

 and when we also bear in mind the enormous development of glacier- 

 ice that took place in all the mountainous districts and northern 

 countries of Europe, it is impossible to believe that the south of 

 Spain could have escaped the influence of a refrigeration so great 

 and general. In the light of all these facts, it ceases to be sur- 

 prising that the Rock of Gibraltar (which, during Pleistocene times, 

 may have stood 1500 or 2000 feet higher) should afford evidence 

 of having at some comparatively recent period passed through colder 

 conditions of climate than it now enjoys. Nor is it uninteresting to 

 observe that just as in the Glacial deposits of Central and Northern 

 Europe (not to mention those of Northern America) we have proofs 

 of former great alternations of cold and genial climates, so in the 

 superficial accumulations of Gibraltar we have evidence of similar 

 vicissitudes — conditions extremely favourable to the formation of 

 coarse agglomerates having occurred at least twice, while the cli- 

 matic conditions of the intervening period apparently did not differ 

 much, if at all, from those which are at present characteristic of the 

 Straits. 



EXPLANATION OF PLATE XXIII. 



Geological map of Gibraltar, on a scale of two inches to one mile. 



Discussion. 



Prof. T. Rupert Jones congratulated the Society on hearing Prof. 

 Ramsay's communication, which he characterized as a typical paper, 

 bringing modern knowledge to bear upon and illustrate earlier re- 

 searches. Before asking for further information upon some points, 

 he would state his objection to the word " agglomerate," which was 

 intended by Lyell to be applied to a volcanic rock, being used by 

 the authors for limestone-breccias. Prof. Jones asked Prof. Ramsay 

 for further information as to the cause of the great differences of 

 dip in the several sections of the rock, differences incompatible 

 with north and south undulations of the strata and referred by Mr. 

 James Smith to a succession of transverse faults from the truncated 

 northern escarpment to the Straits. With these faults, he thought, 

 the caves explored by Capt. Broome and others were connected, and 

 on these the authors had made no remarks. Prof. Jones had also 



