Geological Society. 261 



double stars, the change of their motions would not surprise us ; we 

 should acknowledge them as necessary, and have only to investigate 

 their amount by observation. But light is no real property of 

 mass. The existence of numberless visible stars can prove nothing 

 against the existence of numberless invisible ones. There have been 

 also stars which seemed to possess the peculiarity of a bright body 

 passing over, and which have again lost it ; for example, the star of 

 Tycho. The phsenomena then of the varying motions of the stars, 

 •which are so important for the results of plane astronomy, seem also 

 to possess interest in relation to our knowledge of the physical con- 

 stitution of the universe. 



(Signed) F. W. Bessel. 



GEOLOGICAL SOCIETY. 

 [Continued from vol. xxv. p. 539.] 



November 20, 1844. — A paper was read " On the Geology of 

 Gibraltar." By J. Smith, Esq. of Jordan Hill. 



The great rocky masses terminating Europe on the S.W. and 

 Africa on the N.W., and cut through by the Straits of Gibraltar, con- 

 sist of siliceous sandstones, associated with limestone, chert, shale and 

 coal, all apparently of the oolitic formation. The Gibraltar limestone 

 contains casts of Terebratula fimbria and T. concinna, species found in 

 Britain in the lower oolite. The covering of the older rocks consists 

 of soil, river alluvium, post-tertiary marine sands, and local patches 

 of diluvium. Wherever the covering is removed, the surface of the 

 rock beneath is seen to be water-worn. The rock of Gibraltar is 1470 

 feet high. The southern extremity is marked by a triple series of 

 terraces and inland cliffs, formed by the sea at former levels. Its 

 northern terminates in a perpendicular cliff. The elevated part is 

 divided into three distinct eminences, the effects of different local 

 upheavals. The northern of these (the rock gun) does not appear 

 to have undergone any derangement in its stratification since its first 

 upheaval, although it must have been subjected to many elevations 

 and depressions of level. Its older beds (those of the limestone) dip 

 west at an angle of 20°, and those formed since the elevation are 

 horizontal, remaining in their natural position. In this state the 

 whole of the rock must have remained for a lengthened period, until 

 a second upheaval broke it across, leaving the northern portion in its 

 original position, but lifting the whole of the southei'n 20° more, so 

 that its beds, which formerly dipped 20° west, now dip 40° ; and the 

 fresh deposits, formerly horizontal, 20°. On these deposits, others, 

 formed after the upheaval, rest unconformably. A third upheaval in 

 the same direction, but still further to the south, lifted the rock there 

 about 20° more, leaving the northern and middle hills in their former 

 position, but inclining the southern 60°. Thus we have four distinct 

 epochs ; of the deposits formed during each we have remains, and at 

 Martin's Cave the whole maybe seen in juxtaposition. Immediately 

 under O'Hara's tower, the highest peak, the inclination of the beds 

 to the west is nearly 80°, and a short way to the south of it, they 

 are vertical. Under this point there is, at the height of about 50 



