Of GIBRJLTJR. ' igs 



thinly mixed with minute parts of tranfparent quartz cryftals ; 

 the remaining foot and a half, to the bottom, contained an ag- 

 gregate of water-worn flones, which were from the lize of a 

 goofe's egg to that of a fmall wahiut, and confided of red jaf- 

 pers, yellowifli white flints, white quartz, and bluifli white 

 agates, firmly combined by a yellowilh brown ftaladlitical cal- 

 careous {par. In this breccia I could not difcover any fragment 

 of the , mountain rock, or any other calcareous matter, except 

 the cement with which it was combined. This pot is 940 feet 

 above the level of the fea. 



Upon the weft: fide of the mountain, towards its bafe, fome 

 flrata occur, which are heterogenial to the mountain rock : the 

 firft, or higheft, forms the fegment of a circle ; its convex fide is 

 towards the mountain, and it flopes alfo in that dire(5tion. This 

 ftratum confifts of a number of thin beds ; the outward one, 

 being the thineft, is in a (late of decompofition, and is moulder- 

 ing down into a blackifh brown or ferruginous coloured earth. 

 The beds, inferior to this, progreflively increafe in breadth to 

 1 7 inches, where the Gratification refls upon a rock of an argil- 

 laceous nature. 



This lad bed, which is 17 inches thick, confifts of quartz of 

 a blackifh blue colour, in the fepta or cracks of which are 

 found fine quartz cryftals, colourlefs, and perfe<5lly tranfparent. 

 Thefe cryftals are compofed of eighteen planes, difpofed in hex- 

 angular columns, terminated at both extremities by hexangular 

 pyramids. The largeft of thofe that I have feen does not ex- 

 ceed two-eights of an inch in length : They, in general, adhere 

 to the rock by the fides of the column, but are detached with- 

 out diflSculty. Their great degree of tranfparency has obtain- 

 ed them the name of Gibraltar diamonds. 



At no great diftance from where thefe cryftals are found, 

 upon the fame flope of the mountain, but rather nearer to the 

 level of the fea, a ftratum of argillaceous matter has been laid 



A 2 open 



I 



