|g8 MINERALOGY OF THE PENTLAND HILLS, 



pact felspar. From this valley, ijt may be traced 

 more or less uninterruptedly along Black Hill, 

 ^irk Hill, and Castlelaw, and onwards to the 

 Kirkyetten Hills, where it forms a considerable 

 portion of the striking rocky face named Kirkyet- 

 Xen Craig. In the whole of this course, it is as- 

 gQciated with compact febpar. 



¥11. Claystone-Tuff. 



This rock is composed of cl^ystone, in whicl:| 

 are included apparent fragments, of various sizes 

 and shapes, of clay stone, porphyritic-claystone,^ 

 conchoidal-hornstone, porphy ritic-hornstone, com- 

 pact felspar, and red flint. It is sometimes tra- 

 versed by veins of conchoidal horn^tone and por- 

 phyry ; and these, as well as all the different kind^ 

 'of fragrnents, are of cotemporaneous formation 

 w^ith the claystoiie basis f . The conchoidal-hornT 

 stone sometimes assumes a slaty appearance, and 

 passes into striped jasper : it also passes into clay- 

 stone, compact felspar, aqd into flint. Both the 

 cjaystone and the conchoidal-hornstorie are some- 

 times beautifully dendritic. 



It appears in some instances to rest on conglo- 

 merate, sometimes on clinkstone-porphyry, and is 



^ It is GYident that the formation of trap-tyff must also be 



