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 height 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 however 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; limestone, quartz rock, limestone, schist, limestone.[1] 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 purposes of this paper I made no accurate record of it. It is to be regretted on this account as well as many others, that no geographical
- ↑ Rocks thus situated have by some mineralogists been divided into principal and subordinate beds, but however this distinction may occasionally be found to hold good with regard 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 language 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 others The term interstratified, involves neither obscurity nor hypothesis, and is amply sufficient for the purposes of description, when combined with the relative proportions and positions of the rocks in question.
