122 Outlines of the Mineralogy of the Ochil Hills. [Feb. 



part of which is much decomposed. This limestone varies from 

 an earthy to a highly crystalline structure, resembling if not 

 passing into calcareous spar. 



This is the only instance throughout the whole of the Ochils that 

 I have seen limestone, although I have been assured that other 

 portions of it have been observed at a considerable elevation above 

 the village of Abernethy. On examining the situations to which I 

 Was referred I could discover no traces of limestone, from which I 

 have been induced to suspect that the popular belief is unfounded. 



5. Slate-clay. — Thin scams of a bluish-grey slate-clay, possess- 

 ing the common chai'acters, occur both above and below the lime- 

 stone, separating it from the grey sandstone. 



6. Claystone, — ^^J'his is a very abundant rock, and some very 

 beautiful varieties of it occur in the course of the Ochil Hills. At 

 Lucklaw* it appears to pass into basaltic clinkstone; below Birk- 

 hillf it alternates with sandstone, tuff, and felspar, passing on tlie 

 one hand into the grey sandstone, and on the other, through all the 

 varieties of tuft and clinkstone, to the perfectly compact felspar. It 

 is also found between the Vctts of Muclchart and Alva, below the 

 clinkstone, with which it probably alternates. 



it is fine grained, having a large flat conchoidal fracture, and an 

 uneven cross fracture. It occasionally contains S(?ales of silver- 

 white mica, particularly where it alternates with the sandstone and 

 tuff, as it does below Rirkhill. The colour is »arious, even in the 

 alternating strata ; the most common, however, is between pearl 

 grey and Isabella yellow. It sometimes, though rarely, is amygda- 

 loidal : the cavities of such varieties are filled with green earth and 

 white calcareous spar : crystallized felspar is dispersed throughout 

 the mass. 



The clavstone alternates with the grey sandstone and the tuff, 

 between which it is most probably the connecting link; for it passes 

 almost imperceptibly at its extremities into each of them. It is 

 doubtful vvhether or not the claystone be of older formation than 

 the limestone, as I have seen both in similar relations to the sand- 

 stone. The present location, therefore, of these rocks, in so far 

 as they regard each other, must, until more extended observations 

 shall have been made, be considered as entirely arbitrary. 



7. Tuff.' — A very remarkable tufacious rock occurs above the- 

 clavstone at the base of Birkhill, and at the western extremity of 

 \\'ormit Bay. In botli of these situations it alternates with the 

 sandstone and claystone. In no other part of the Ochils have I 

 observed a similar arrangement. 



This tuff is coarse, inclosing portions of felspar, which is some- 

 times lost in the prevailing mass. The chief colours are flesh-red 

 and Isabella yellow. It ap'pears to be one of the newest members 

 of tlic sandstone series, and tliere is a gradual passage from it to 



•» Tl?is is a small hill between Ciipar and Parton Grains. 



; An eminence about five roiles to the weetnaril of WoodUavro. 



