and Sandstone at Stirling Castle Rock. 307 



The sandstone bed Itself consists of different lamina:, varying . 

 in colour, but generally slate-coloured, yellowish, and grey. The 

 two lowermost and thickest beds differ little or nothing in texture, 

 colour, or quality, from ordinary calcareous sandstones, and they 

 are (as the drawing shews) of considerable thickness compared 

 with those which immediately follow them. 



These thinner beds are separated from each other by laminse, of a 

 clay slate, very much confounded with the sandstone, and those 

 two substances alternate frequently and irregularly, till they ap- 

 proach the thicker beds which lie in contact with the greenstone. 

 As they approximate to it they become more indurated, and assume 

 a texture approaching to that of hornstone. The lowermost of 

 the two upper beds thus exhibits a kind of hornstone of which the 

 fracture is occasionally granular, and occasionally passes into the 

 splintery and conchoidal. The uppermost bed exhibits the cha- 

 racters of perfect hornstone. It is of an ochre-brown colour, its 

 fracture is conchoidal, or splintery, with an even shining surface, 

 and the thin fragments transmit light. 



As the specimens are before the Society, I need not enter into 

 more minute details, particularly as, if taken together with the draw- 

 ing, they will shew the regular gradation from the ordinary cal- 

 careous sandstone to the perfectly characterized hornstone. I may 

 just be allowed to point out the resemblance which this change 

 bears to that gradation from sandstone to a jaspideous rock, which 

 occurs in a similar situation at Salisbury Craig. Considering merely 

 the mechanical position of the sandstone, I confess myself unable 

 to comprehend how by any combination of accidental abrasion or 

 fracture, and successive deposition by precipitation, the present, 

 and similar appearances can be produced. Although the projecting 

 portion of the sandstone might have been able to maintain its place 



2 cl2 



