IN GLEN TILT. 



S59 



differed also in my description of the facts, Professor Jameson's 

 extensive experience, and acuteness in the discrimination of 

 minerals, might seem to claim submission on my part ; did I 

 not consider that his observations must have been liable to a 

 certain degree of bias from a favourite theory, — a bias, from 

 which I can scarcely flatter myself that my own were kept en- 

 tirely free *. 



134. I proceed now to describe the rocks in the bed of the 

 Tilt, as far as the junction of the Tarff, and shall subjoin some 

 observations on the mountains to the north-west of the 

 Glen. 



1S5. For about a mile below the junction of the Chlochan, 

 the channel of the Tilt is perfectly straight, and the bottom of 

 the Glen is contracted to its breadth. The channel is here 

 formed on both sides by rocks of a singular aggregate, ap- 

 proaching in its characters to sienitic greenstone. The colour 

 of the mass is a dark greenish-grey, but varying according to 

 the proportion of its ingredients, which are intimately mixed, 

 and seem to be hornblende, felspar, sometimes compact, and 

 sometimes crystallised, steatite or chlorite, and a good deal of 

 carbonate of lime, or magnesia, perhaps both. The presence 

 of these last ingredients is inferred from its effervescing brisk- 

 ly with muriatic acid. It may not be improper to consider 

 the mass as a compound of hornblende, felspar, and compact 

 dolomite, with a little chlorite, or steatite. Its hardness is not 

 great, but it is very tough under the hammer. It is neither 



Z z 2 stratified, 



* See note C. 



