46 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



nation they are kept by the winds from the east, which are the only 

 ones which reach them. 



3. 



In the above diagram (3), which represents a section from west 

 to east of Middle Hill, a is the limestone; 6, thin beds of sandstone 

 resting unconformably upon it at an angle of 19°; cc, beds of sand- 

 stone and sand formed subsequently to the second upheaval, but 

 when the sea-level was different ; dd^ the present beaches; e, blown 

 sands. With the exception of the limestone, the mineral composi- 

 tion of all these beds is the same, consisting of comminuted parti- 

 cles of limestone and quartz, h and c have been indurated into 

 thin crumbling strata; they contain fragments of sea-shells, but 

 although I have found none sufficiently entire to ascertain the spe- 

 cies, they have all the appearance of being recent. 



A third upheaval in the same direction, but still further to the 

 south, has again tilted up the beds in that part of the rock about 

 J 9°, leaving the northern and middle hills in their former position, 

 but inclining the strata to the south to 57° ; the line of division is 

 marked by an indentation to the south of the signal-post, called in 

 Spanish La Quehrada, or broken ground. We are now arrived at 

 the fourth epoch in the history of the rock ; and in this locality we 

 find deposits belonging to each. At one spot a little to the east of 

 Martin's Cave, and looking towards it, the whole of them may be 

 seen in juxtaposition. 



4. 



O'Hara's Tower. 



In the diagram marked (4), which represents a section from west 

 to east of the third or O'Hara's Tower height, the secondary lime- 

 stone («), originally level, has been lifted up by repeated upheavals 

 to an angle of 57° ; the beds {b) formed at the base of the rock 

 subsequently to the first upheaval, have been lifted up by the second 

 and third upheaval to an angle of 32°. As the two preceding move- 

 ments were of 19° each, had the beds at b been originally hori- 

 zontal, the angle would have been 38° ; they must therefore have 

 sloped outwards 6°, which is about the inclination of the present 



