NICOL SOUTHERN GRAMPIANS. 181 



mary strata. In my ' Guide to the Geology of Scotland/ in 1844, I 

 pointed out the close resemblance of some parts of these formations 

 to the Silurian strata in the South of Scotland, and indicated that 

 they were merely the metamorphosed representative of the latter. 

 In a paper read before the Geological Society in 1849 I again stated 

 this opinion, and specially noted the " band of clay-slate from Stone- 

 haven to Arran as forming the continuation of the Silurian beds in 

 the south, rising up on the other side of the synclinal valley in which 

 the Carboniferous strata of Scotland have been deposited"*. The 

 same views of the identity of the crystalline strata in the North of 

 Scotland with the Silurian deposits in the South have been expressed 

 by me on many subsequent occasions f, and may thus have in some 

 points influenced the statements given in the following paper. 



2. Object of the Paper. — My principal object in describing these 

 sections is to examine the relation to each other of the three great 

 formations, the Clay-slate, the Mica-slate, and the Gneiss, which, 

 with some subordinate groups, as the Quartz-rock and Chlorite -series 

 of Macculloch, have hitherto been regarded as composing the chief 

 stratified masses in the Scottish Highlands. These formations, 

 " founded on the great relations which rocks bear to each other and 

 to the general structure of the earth "J, have been recognized with 

 nearly identical characters in the most distant regions of the globe, 

 thus showing that they are not mere capricious distinctions of local 

 observers, but true constituents of the crust of the earth §. The 

 order originally assigned to these formations by Werner — of Gneiss 

 in the lowest position, followed by Mica-slate, and this by the Clay- 

 slate — has usually been adopted by geologists, though some re- 

 markable exceptions to this order have been long known. To some 

 of these I adverted in 1844, and again in a paper read before the 

 Geological Society in 1855, in which I endeavoured to explain the 

 phenomena on the supposition of a reversal of the beds. The 

 following sections will show how far this view can still be main- 

 tained || . 



* Guide to the Geology of Scotland, pp. 128, 139, 249 ; Quart. Journ. Geol. 

 Soc. vol. vi. (1849) p. 60. 



t See especially " On the Geol. of Cantyre," Quart. Journ. Geol. Soc. vol. viii. 

 (1852) pp. 422, 423 (the substance of this paper was read at the Meeting of 

 the British Association at Edinburgh, in August 1850) ; " On Easdale and Oban," 

 id. vol. xv. (1858) pp. 112, 116 ; Note to Geol. Map of Scotland, Edinb. 1858. 



X Macculloch, Geological Classification of Rocks (1821), p. 3. In that work 

 the different varieties of rocks composing each formation are fully described, and 

 perhaps undue importance ascribed to them. See also his ' Western Isles,' vol. ii. 

 p. 353, note. 



§ It is enough to mention Humboldt's Essai geognostique sur le Gisement de 

 Roches (Paris, 1826) among the older, and Naumann's elaborate ' Lelirbuch der 

 Geognosie' among the newer foreign works, in proof of this universal recogni- 

 tion of these formations. Dr. Ami Boue, from his knowledge of Scottish rocks, is 

 an unexceptional witness to their agreement with those of foreign countries. 



|| See Guide to Geol. of Scotland, p. 169 ; " Section of the Eastern Grampians," 

 Quart. Journ. Geol. Soc. vol. xi. p. 547. Even in 1821, in his ' Treatise on Rocks,' 

 p. 92, Dr. Macculloch had pointed out this fact, like many others which have been 

 claimed as new discoveries. 



