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We are indebted to Major Imrie for a most useful and interesting mi- 

 neralogical description of the mountain of Gibraltar, in the fourth volume 

 of the Transactions of the Royal Society of Edinburgh, p. 191, the whole 

 of which is highly worthy your examination. That which most par- 

 ticularly demands your attention I have here introduced. 



The eastern side of the mountain, mostly consisting of a range of pre- 

 cipice, terminates with a bank of sand in the Mediterranean. The 

 southern extremity terminates in the sea, with a rapid slope, and ibrms 

 Europa Point. On the Western side, this peninsula-mountain is bounded 

 by the Bay' of Gibraltar; and, upon the North, it is attached to Spain 

 by a low sandy isthmus, the greatest elevation of which, above the 

 level of the sea, does not exceed ten feet ; and its breadth, at the base 

 of the rock, is not more than three quarters of a mile. This isthmus 

 separates the Mediterranean on the East, from the Bay of Gibraltar on 

 the West. 



The principal part of the rock consists of a grey dense marble, in some 

 parts of which are imbedded testaceous bodies, in a spathose state. As 

 is almost always the case, where this species of rock constitutes large 

 districts, the rock of Gibraltar is cavernous ; the caverns being beset 

 with stalactitic, and other calcareous infiltrations. On the surface of 

 the rock are seen pot-like holes, hollowed out by the attrition of gravel or 

 pebbles, set in motion by the rapidity of. rivers, or currents in the sea, 

 some of the pebbles now remaining in them. From this phenomenon, 

 Mr. Imrie concludes, that however high the surface of this rock may now 

 be elevated above the level of the sea, it has once been the bed of agitated 

 waters. 



With respect to the fossil bones found in this rock, the general idea 

 concerning them is, that they are found in a petrified state, and inclosed 

 in the solid calcareous rock; but these are mistakes which Mr. Imrie 

 thus aims at correcting : " In the perpendicular fissures of the rock, 

 and in some of the caverns of the mountain (all of which afford evident 

 proofs of their former communication with the surface), a calcareous con- 

 cretion is found, of a reddish brown colour, with an earthy fracture and 



