THE GEOLOGY OF GIBRALTAR. 517 



is more than a glance needed to show that the agglomerate has been 

 exposed for a prolonged period to the action of the weather, and 

 that it is now, and must for a long time have been, wearing away 

 much more rapidly than it can possibly be accreting. "We need 

 only point to the rugged aspect of the mass at Buena Yista, where 

 the agglomerate has been excavated into gullies and ravines from 30 

 to 50 feet and more in depth and breadth. It will further be 

 shown in the sequel that platforms or terraces have been cut in this 

 rock by marine erosion, so that in every respect the Buena- Yista 

 agglomerate bears the stamp of great antiquity. 



As further proving that this agglomerate could not have origi- 

 nated under present conditions, we may point to the fact that the 

 loose stones which are scattered sparingly over the surface of the 

 limestone at the higher levels of the Bock, and which are gathered 

 here and there into gullies by the action of the winter torrents, are 

 not as a rale so sharply angular as the fragments in the agglo- 

 merate. More than this, it is evident that heavy accumulations of 

 agglomerate occur, spread over wide areas, to which it is impossible 

 that angular stones can, under present conditions, make their way 

 from the heights of the Rock. It is quite obvious that a much 

 greater force than that exerted by the present winter torrents was 

 needed to bring down from the heights those large blocks of lime- 

 stone that occur so plentifully in the agglomerate that stretches 

 from the Mount down to the sea at Rosia. "We were informed by 

 Mr. Roberts and others, who have been long resident in Gibraltar, 

 that a fall of rock from the cliffs is of the rarest possible occurrence. 

 What the inhabitants chiefly fear are the sudden torrents of the 

 rainy season, which now and then sweep down quantities of loose 

 materials, grit, earth, and small stones. In short, it is evident that 

 although stones and blocks, loosened by the action of rain and 

 percolating water, must sometimes be launched from the higher 

 parts of the Rock, yet the agglomerates that lie at its base and upon 

 its flanks do not belong in the main to modern times, but owe their 

 origin to conditions which no longer prevail. 



At present frost may be said to be unknown in Gibraltar. The 

 mean temperature of the coldest month (February) is 54°-2, and the 

 lowest minimum reached in six years (1853-59) was 32 0, 7. It is 

 very rarely, indeed, that the temperature falls so low. We were 

 told that a thin pellicle of ice had once and again been observed 

 upon a pail of water at the Signal Station ; and Mr. Roberts in- 

 formed us that there is a legend to the effect that, many years ago, 

 i C e -j-^th of an inch thick had been seen at the North Front. The 

 fact that these phenomena are specially noted at Gibraltar only 

 serves to show how unfrequently they occur. With severe frosts in 

 winter the inhabitants would doubtless have a lively time of it, from 

 the frequent discharge of blocks and stones from the steep broken 

 ground and cliffs at the foot of which the town is built. It appears 

 to us, however, that it was precisely under such climatic conditions 

 as these that the great agglomerates were formed. The rocks in 

 question speak to us of strong frosts which broke up the limestone 

 along the crest of the Rock, and showered it down in sharply- 



