422 Mlncralog'ical Ohservations in Galloway. [June, 



in beds of a ^reat thickness. I measuicd one of the hods of the 

 gneiss liack from ilic granite toward the soiitii-cast, and found it lo 

 be not less tlian 25 yards thick. At this place there are a ijumber 

 of loose blocks of the rock which rests immediately on the granite 

 of the Louran, and which some have termed an altered rock, or 

 greywacke changed by the influence of the granite in a state of 

 fusion, but which I think is better denominated a fine-grained or 

 compact gneiss (the appellation given it by Professor Jameson). I 

 measured one of the blocks of this rock, "and found it to be five 

 feet thick, and nearly double that in length. I cannot therefore 

 understand a passage of Sir James Hall's ingenious paper in the 

 last published volume of the Transactions of the Royal Society of 

 Edinburgh, entitled, On the Conditions of Strata and their meeting 

 with Granite, wherein he says, speaking of the Louran, " In the 

 immediate vicinity of the granite, to the distance of Sifoot or iivo, 

 and not more, the stratified matter has in many cases assumed a 

 highly micacious character, so as to deserve the name of mica slate, 

 or perhaps gneiss." This passage is quite inconsistent with the 

 existence of loose blocks of that rock five feet thick, and still more 

 so with strata of it 25 yards in thickness. Indeed, if I mistake not 

 greatly, at the very place where Sir James, some years ago, with 

 such laudable zeal for the interests of science, and such indefa- 

 tigable perseverance, denuded a large portion of the rock on the 

 east side of the Louran, at the place called Windy Shoulder, there 

 are to be seen strata of this finegrained or compact gneiss, (or, as 

 Sir James chooses to term it, " stratified matter assuming a highly 

 micacious character,") of a thickness far beyond what he states. I 

 had here an opportunity of observing the very interesting granite 

 veins of which Sir James has given so accurate an account, and 

 which are thought by some to aflFord a strong confirmation of tlie 

 truth of the Huttonian theory, but which others view in a different 

 light, and consider as nothing more than contemporaneous veins. I 

 found a variety of the fine-grained gneiss among the loose blocks I 

 already mentioned near Strone Loch, with the mica much more 

 distinct and abundant than any I had before seen in the district. 



8. ]\Iy next observation on the bearing and dip of the strata was 

 on the brink of Strone Loch, very near the lower end of it, from 

 whence the river Dee issues. Here I found compact gneiss strata 

 running N.N.E. ; inclination about 70, and dip towards the south- 

 east ; of a great thickness — upw-ards of 40 yards thick. 



9. My next observation was about 200 yards below the foot of 

 Strone Loch, where the compact gneiss crosses the river in vastly 

 thick masses of nearly vertical strata, dipping a little however to 

 the south-eastward, and running in a direction from N.N.E. to 

 S.S.A^'. I was desirous, if possible, to discover some place where 

 the rock was sufficiently exposed to enable me to see the junction 

 of the gneiss with the greywacke : and I conceived that the bed of 

 the river here was the most likely to afford me such an opportunity. 

 I therefore traced it down about a mile, and at last I found a rock 

 laid bare on the portji side of the Dee^ where the compact gneiss 



