MINERALOGY OF THE PENTLAND HILLS. 195 



bit a very deep- grooved surface : this is strikingly 

 the case with the felspar of Braid Know. It is 

 sometimes porphyritic, and then it contains im- 

 bedded crystals or grains of felspar ; sometimes 

 also scales of mica, crystals b£ augite, and of 

 common quartz, or of rock-crystal. A remark- 

 able variety of this mineral occurs near Hab- 

 bie's How and other parts of the group, in whicTi 

 beautiful globular concretions of light red-co- 

 loured felspar are imbedded in dark- red felspar. 

 These concretions are from one-sixth of an inch, 

 to an inch in diameter. Other globular concre- 

 tioris occur in the felspar ; these are composed of 

 concentric lamellar layers of red felspar, and of a 

 green-coloured substance, which is probably very 

 minute granular hornblende, either pure or inter- 

 mixed with felspar. Both these kinds of concre- 

 tions are evidently of cotemporaneous formation 

 with the felspar in v/hich they are contained, be- 

 • cause thfey are principally composed of that sub- 

 stance, and exhibit no marks of attrition' ; on the 

 contrary, are to be observed gradually passing into 

 the surrounding mass. Compact felspar is observ- 

 ed passing, on the one hand, into hornstone, and on 

 the other into claystond It occurs in beds, and 

 in cotemporaneous masses several feet square in 

 conglomerate, at Habbi'e's How ; and at the same^ 

 place, it appears to rest on transition clay- slate. 



It occurs abundantly in Black Hill, Bield Hill, 

 Kirk Hill, 'Capelaw, and Castlelaw, where it is 

 more or less frequently associated with claystone. 

 It also occurs, but less frequently and abundantly;,' 



