264 Dr. Mac Culloch on the Geology of Glen Tilt, 



It is not far below this place, but at a distance which I have 

 neglected to note, that a great portion of a limestone bed will be 

 found crossing the river. It is much contorted, and is also reticu- 

 /ated with a few granite veins. Here the alternation of the lime- 

 stone with the quartz rock is also visible, and they cross the river 

 together. The limestone Is in this place uncommonly hard, and 

 in its composition very siliceous. Its external aspect where it 

 is worn by the action of the water, Is not much unlike that of a 

 granite or porphyry, and it has in fact been sometimes mistaken 

 for one or other of these rocks. Continuing to descend nothing 

 remarkable occurs till we arrive within about two miles of Forest 

 lodge, where a rock like those last mentioned, traverses 

 the bed of the river. This rock consists of a great mass of 

 red granite so mixed with quartz rock and hornblende schist, that 

 neither pen nor pencil can describe their confusion. Limestone 

 may be observed both at its upper and lower edge, and this is 

 traversed and reticulated by small granite veins. The whole mass 

 occupies a space of about 150 yards. It is proper to remark here, 

 that the blanks which occur in this account of the bed of the river 

 are such as In general arise from its course being over a bed of 

 alluvial matter which covers and conceals the fundamental rock, 

 while in other cases they arise from those portions of the natural 

 bed which are visible being trivial or unimportant, or from the state 

 of the water which prevented its bottom from being seen. 



The next, and of all perhaps the most remarkable rock to be 

 observed in the course of the Tilt, occurs at a bridge a short distance 

 above Forest lodge. A large mass of red granite is first seen occu- 

 pying the bed of the river for a considerable space both above and 

 below that bridge. Associated with this mass of granite are various 

 rocks> so disposed and intermingled that neither description, nor draw- 



