THE PENTLANDS. 81 



quartz-rock, and in others becoming a conchoidal hornstone. 

 At the western extremity of the valley, and on the south of 

 Black Hill, a natural section exhibits numerous alternating 

 strata, of a very fine granular brown sandstone and slate. 

 The mineral characters of the latter are in some places si- 

 milar to those of the slates associated with grey wacke : if, 

 however, its position, in regard to the rocks with which it 

 is connected, be observed, and its aspect compared with that 

 of slates whose place in the carboniferous group is more ap- 

 parent, its geological age becomes sufficiently evident. In 

 the course of the North Esk river, from its rise in the Dod- 

 rig to Carlops, there are many fine sections of this slate ; 

 it is found alternating with the coarse sandstone conglome- 

 rate of the Pentlands, and in some places with the sandstone 

 of the coal series. At Habbie's How the slate, which is 

 vertical and ranges S. W- and N. E., rests upon the com- 

 pact felspar of Black Hill, and throughout its whole extent 

 exhibits evident marks of having been at one time sub- 

 jected to energetic upraising actions. Conglomerate forms 

 the western extremity of the valley of Glencorse ; it dips to 

 the W. by S. at 15°, being thus in a position anything but 

 conformable with the slate. As we have already stated, how- 

 ever, that the synchronism of deposition of these two rocks 

 is well seen in other parts of the Pentlands, the causes of 

 this may in all probability be referred to the upburst of the 

 Plutonic rocks, with which both are so intimately connected. 

 On examining the conglomerate, as exposed by the cascade 

 of Habbie*s How, it is found traversed by minute veins of a 

 compact felspar, similar to that which is associated with the 

 slate ; it is however more compact, and thus affords another 

 instance of that change of mineral character which the ignige- 

 nous rocks evince, when they traverse Neptunian strata in the 

 form of veins, or come in contact with them as overlying masses. 



VOL. VII. f 



