Webster on Calton Hill. 233 



The wacke has a greenish gray colour, which is pretty uni- 

 form. The fracture is nearly even and earthy, it is soft, yield- 

 ing 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 

 concretions, having a tendency to the prismatic form. This 

 wacke fuses with difficulty before Brooke's blow-pipe. Spe- 

 cific gravity not determined, as it falls to pieces on being moist- 

 ened. 



The sandstone is for the most part gray, in some parts spot- 

 ted 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 architec- 

 ture. 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, gradually decreasing till less than an inch in thick- 

 ness at the other, or they may even be lost entirely, and gra- 

 dually regain their former size ; and it is not improbable that 

 these beds of sandstone will be found to continue on towards 

 the adjoining hills of Salisbury Craig and Arthur's Seat, pass- 

 ing 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 admit- 



