306 Dr. Mac Cu LLOc H on the Geology of Glen Tilt. 



specting a cause can be deduced from these appearances. The beds 

 of limestone which I have thus in a general manner described on 

 account of their perfect resemblance through»their whole course, 

 continue with scarcely any alteration as far as the burn of Glenmore, 

 extending upwards to a hei-ght in the hill similar to that which they 

 have at the western end of the ridge. The alternation of the beds 

 with schist and quartz rock is howe\'er more visible on the sides of 

 the Tilt in this part of its course ; and at the river Aldianachie 

 in particular, there is so be seen an alternation in this order ; lime- 

 stone, quartz rock, limestone, schist, limestone.* The beds of 

 limestone do not cease at the burn of Glenmore, but after 

 crossing it they are less continuously visible, while at the same 

 time they lose the almost rectilinear course which their elevated 

 edges have hitherto preserved. A bed of white marble is found 

 among them at Fealair, and some rolled stones of pink marble in 

 the channel of the river point out also the probable existence of a 

 bed of this colour. Alternations of limestone with quartz rock and 

 schist continue to be seen in this southern ridge of Glen Tilt 

 towards Scarsough, but the pursuit being unnecessary for the pur- 

 poses of this paper I made no accurate record of it. It is to be re- 

 gretted on this account as well as many others, that no geogra- 



* Rocks thus situatedTiave by some mineralogists been divided into principal and subordi- 

 nate beds, but however this distinction may occasionally be found to hold good with re- 

 gard to some of the rocks so enumerated, yet as it is by no means a distinction universally 

 existing, it ought not to be erected into a general rule, since it increases the number of 

 artificial divisions, and offers a convenient and unmeaning phraseology instead of the lan- 

 guage of accurate description. Subordination implying inferiority or dependence, it should 

 follow that the one rock was in all cases either necessarily less in quantity, or in some way 

 dependent on the other. The term interstruiijied, involves neither obscurity nor hypo- 

 thesis, and is amply sufficient for the purposes of description, when combined with the 

 relative proportions and positions of the r^cks in question. 



