COMPACT FELSPAR OF PENTL AND HILLS. 6lJ 



transition and floetz rocks of different kinds. The 

 transition formation constitutes the fundamental 

 rock, which consists of grey wacke, grey wacke- 

 slate or transition- slate • displayed in vertical strata. 

 Over these, apparently in an unconformable and 

 overlying position, occur rocks of conglomerate, 

 sandstone, trap-tuff] a tuff with a base of clay stone, 

 clay stone, compact felspar, porphyroid, or porphy- 

 ritic claystone, clinkstone, basalt and greenstone. 

 It does not appear that Professor Jameson has 

 hitherto ascertained whether these floetz strata 

 constitute one or more different floetz formations. 



One of the most striking rocks in the above 

 described series is the compact felspar, which oc- 

 curs so abundantly in some places as to form near- 

 ly the whole mass of several hills. The specimen 

 employed for analysis exhibited the following 

 characters. 



Its colour was flesh red, its fracture minute 

 foliated, its internal lustre glimmering, its frag- 

 ments sharp edged ; it was translucent on the 

 edges, semi hard, brittle, fragile; its specific gra- 

 vity was 2.497. 



The Pentland Hills exhibit the first known 

 example of compact felspar constituting moun- 

 tain-masses. The same subspecies occurs also in 

 primitive country, in beds, from one to eight or 

 ten feet thick, as at Coriarick, and other pacts of 

 the Highlands of Scotland. It occurs also in tran- 

 sition mountains in the south of Scotland. But in 

 neither of these situations is it so abundant as in 



