306 Dr- Mac Culloch on the Junction of Trap 



It forms a large stair, having its escarpement towards the west, 

 and its inclination similar to that of the great rocks which are 

 not only found in the vicinity of Edinburgh, but are to be seen 

 rising above the general level through the whole interval between 

 Edinburgh and Stirling. The hill of Stirling, and that of Crai^ 

 Forth, are, I believe, the most western of this class of rocks, which 

 are connected here, as at Edinburgh, with the coal district. 



It was in cutting a new road through the castle hill that the 

 appearance in question was laid bare. 



The trap stratum consists of a dark blueish black compact green- 

 stone, varying to umber brown, and it is accompanied by tufo ; but 

 the former alone is in contact with that part of the sandstone 

 stratum which is exposed. 



On inspecting the drawing, it will be seen that the sandstone 

 stratum has been split into two parts in the direction of its stratifi- 

 cation. The upper portion is then separated by a perpendicular 

 fracture, and bent upwards, terminating abruptly. It is in this 

 position involved, supported, and covered by the greenstone. 

 The broken end is irregularly fractured, but all its cavities are per- 

 fectly filled up with greenstone. The different laminas of which 

 the sandstone stratum is composed, are not broken to accommo- 

 date themselves to this new position, but are irregularly waved 

 and bent, preserving their continuity every where. 



A little additional disturbance appears on the lower side of the 

 bent portion, as if formed by the separation of fragments ; but 

 the drawing will render the appearance more intelligible than any 

 description could do. The state of the rock did not, when I was 

 there, allow me to examine the other portion of the upper part of 

 the bed from which the broken end had been disrupted : future 

 operations on the rock may hereafter lay bare further portions to 

 illustrate this interesting appearance. 



