256 Dr. Webster on the Calton Hill, fa. [Oct, 



12. Bituminous shale. 15. Wacke. 



13. Wacke. 16. Bituminous shale. 



14. Bituminous shale. 17. Sandstone. 



The wacke has a greenish-grey colour, which is pretty 

 uniform. The fracture is nearly even and earthy, it is soft, 

 yielding readily to the nail, and has a feebly shining streak. A 

 slight stroke with the hammer causes the mass to separate in 

 fragments of various size, the surfaces of which are often smooth 

 and shining, each bed being composed of large distinct concre- 

 tions, having a tendency to the prismatic form. This wacke 

 fuses with difficulty before Brooke's blow-pipe. Specific gravity 

 not determined, as it falls to pieces on being moistened. 



The sandstone is for the most part grey, in some parts spotted 

 red and brown, forming, as the section represents, the last 

 stratum seen ; the beds of sandstone are but a few inches in 

 thickness, and the last (17) becomes less than an inch; it is 

 probable, however, from the relative situation, from the dip and 

 direction, that these strata are a continuation of others seen on 

 the other side of the hill, where they are of sufficient thickness 

 to have been quarried for the purposes of architecture. The 

 beds of all rocks we know vary greatly in different parts, and it 

 is not unusual for them to be some feet at one extremity, gra- 

 dually decreasing till less than an inch in thickness at the other, 

 or they may even be lost entirely, and gradually regain their 

 former size ; and it is not improbable that these beds of sand- 

 stone will be found to continue on towards the adjoining hills of 

 Salisbury Craig and Arthur's Seat, passing under the greenstone 

 and trap tuff. 



The bituminous shale presents the usual characters ; inter- 

 mixed with it are numerous nodules of the common clay iron- 

 stone, the colour of which is a yellowish-brown ; these also 

 frequently present characters common to the three substances, 

 and throughout the beds, the passage from the one to the other 

 is distinct. Whatever may be the opinions in regard to the 

 origin of bituminous shale, there can be but one in regard to that 

 of sandstone ; and this has lately received no feeble support 

 from the account given us by Dr. Paris, of a formation of this 

 rock on the coast of Cornwall, where, says he, " we actually 

 detect nature at work; and she does not refuse admittance into 

 her manufactory, nor conceal, with her accustomed reserve, the 

 details of the operations in which she is engaged." 



From the appearances which have been thus briefly noticed, 

 no impartial geologist, we should imagine, would infer the 

 volcanic origin of any portion of this formation ; and if the 

 aqueous origin of sandstone can be established, that of the wacke 

 must be the same. 



