148 DE. THOMAS STBERY HUNT ON THE 



observers made it clear that in tlie reo-ion in question were portions of two gneissic series, — 

 an older or granitoid gneiss, like that of the western coast, and a younger, very distinct 

 in type, which has been variously designated as Upper Pebidian, Grrampian and Caledo- 

 nian, and is that described by me in 1811, and again in 1881, as of the "White Mountain 

 or Montalban type. This, the younger gneissic series of Murchisou and Giekie, was clearly 

 established to be of great thickness, and older than the fossiliferous Cambrian, which it is 

 brought to overlie by a series of great folds, oA-erturned to the west, and accompanied by 

 parallel faults, with i^pthrows on the east side, as shown by Hicks in Eoss and Inverness 

 shires, as well as by Callaway in Assyut, and by Lapworth in Eriboll. 



§ 192. The concordant and independent results of the eminent observers just named 

 having thus demonstrated the fallacy of the views of Murchisou and Griekie that the 

 gneiss which in the Highlands overlies the fossiliferous strata, is a still younger paleozoic 

 series in an altered condition, the Greological Survey of Great Britain, of which Giekie is 

 now Director, undertook in 1883 and 1884, a re-examination of the region in question. 

 The result of this has completely disproved the former statements of Murchisou and 

 Giekie, aud has confirmed those of the new school. The Director of the Geological Survey, 

 in a note very recently published,"' tells us that he has " found the evidence alto- 

 gether overwhelming against the upward succession, which Murchisou believed to exist 

 in Eriboll, from the base of the Silurian strata into an upper conformable series of schists 

 and gneisses," and adds : " That there is no longer any evidence of a regular conformable 

 passage from fossiliferoixs Silurian c[uartzites, shales and limestones upwards into crystal- 

 line schists, which were supposed to be metamorphosed Silurian sediments, must be 

 frankly admitted." The same conclusions are also reached by Giekie from the re- 

 examination of the similar sections in Eoss-shire, previously described by himself in 

 accordance with the views of Murchisou. 



The preliminary Eeport of the surveyors, Messrs Peach and Home, which is sub- 

 joined to the Director's note, shows the same structure as was already described by the 

 late observers, namely, overturned folds and great faults, with lateral thrusts westward, 

 by which the gneisses are made to overlie the fossiliferous strata, — the horizontal dis- 

 placement of the gneisses to the west, which are superimposed on the Cambrian rocks, 

 being, in some cases, according to Giekie, not less than ten miles. 



§ 193. Giekie notices the distinction between the older or granitoid gneiss, portions 

 of which also appear in the Highlands, and the upper gneissic and mica-schists series, the 

 pre-paleozoic age of which was shown by the observations alike of Hicks, and of Calla- 

 way and Lapworth. He calls attention to the laminated and schistose structure developed 

 by the great pressure and friction along the lines of movement in gneissic and hornblendic 

 rocks, and also to similar changes produced by the same agency in detrital rocks, such as 

 arkose. Both of these structural alterations are apparently included by Giekie under the 

 head of what he calls a " regional metamorphism," — a misapplication of the term likely 

 to confuse the reader, since local structural changes, induced by mechanical movements in 

 ancient crystalline rocks, have nothing in common with that mysterious process which 

 has been supposed by the metamorphic school to generate similar crystalline rocks from 

 uncrystalline sediments. As regards the changes wrought by the same agency on detrital 



=" Nature, Nov. 13, 1884, xxxi, 22-35. 



