Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/315

 Survey of Scotland exists on which reliance can be placed. The errors are in fact beyond enumeration. It would otherwise be a desirable object to trace the real line of direction taken up by this elevated edge of limestone through the long course I have pointed out: but it must be reserved for future examination.

Resuming now the left hand ridge of Glen Tilt at the point where the limestone terminates, the remainder of the task of description is easy. The whole mountain of Ben Gloe is one mass of quartz rock, with scarcely any notable quantity of schist interstratified with it. It is the immediate boundary therefore of the limestone bed, and from the relative position of both, it must consequently be considered as lying above the limestone. The extent of this rock towards the cast is considerable, since it stretches into Mar, and occupies a great part of Glen Shee. To the west it soon disappears, or at least its continuity is broken, since on the west side of the Garry it is only found in alternation with schist. To the south of Ben Gloe this rock is once more seen alternating with limestone, which is again succeeded by the mica slate, and this without further changes, except a gradation into clay slate, terminates at the well known boundary of the secondary strata near Dunkeld and Blairgowrie.

The contortions and the conglomerate aspect of some of the beds are the most remarkable circumstances respecting the quartz rock of Ben Gloe; the former proving that quartz rock, like the schists with which it is associated, has been in a flexible state, and the latter proving beyond doubt the partially mechanical nature of this deposit. Besides these it produces three coloured varieties of quartz, pink, amber brown, and blueish grey; the former equalling in colour the most beautiful varieties of that well known substance.

I have reserved to this place what remains to be said concerning