vzoo MINERALOGIOAL DESCRIPT'ION 



bined. In filTures, narrow and contraded, I found the concretion 

 pofleffing a great degree of hardnefs at fix feet from the furface ; 

 but in other fituations more extended, and where a larger quan- 

 tity of the materials had been accumulated, I found it had not 

 gained its greateft degree of adhefion at double that depth. In one 

 of the caves, where the mafs of concretion is of confiderable fize, 

 I perceived it to be divided into different beds, each bed being co- 

 vered with a cruft of the flaladitical ipar, from one inch to an 

 inch and a half in thicknefs, which feems to indicate, that th^ 

 materials have been carried in at variovis periods, and that thofe 

 periods have been very remote from each other. 



At RoCa Bay, upon the weft fide of Gibraltar, this concre- 

 tion is found in what has evidently been a cavern, originally 

 formed by huge xinfliapely maffes of the rock, which have tum- 

 bled in together. The fifTure, or cavern, formed by the difrup- 

 tion and fubfidence of thofe maflTes, has been entirely filled, up 

 with the concretion, and is now expofed to full view by the 

 outward mafs having dropped down, in confequence of the en- 

 croachments of the fea. It is to this fpot that ftrangers are ge- 

 nerally led to examine the phsenomenon ; and the compofition, 

 having here attained to its greateft degree of hardnefs and foli- 

 dity, the hafty obferver, feeing the bones inclofed in what has 

 lb little the appearance of having been a vacuity, examines no 

 further, but immediately adopts the idea of their being incafed 

 in the folid rock. The communication from this former chafm, 

 to the furface from which it has received the materials of the 

 concretion, is ftill to be traced in the face of the rock, but its 

 opening is at prefent covered by the bafe of the line wall of the 

 garrifon. Here bones are found that are apparently human j 

 and thofe of them that appear to be of the legs, arms, and ver- 

 tebrae of the back, are fcattered among others of various kinds 

 and fizes, even down to the fmalleft bones of fmall birds. I 

 found here the complete jaw-bone of a flieep ; it contained its 



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