Page:Science vol. 5.djvu/102

SCIENCE.

[VuL. v.. No. lOLI groups of crystalline schists of the Atlantic belt in North America, I declared, in an address before the American association for the advancement of science, in 1871, my conviction that the crystalline schists of the Scottish Highlands "will be found … to belong to a period anterior to the deposition of the Cambrian sediments, and will correspond to the newer gneissie series of our Appalachian region." My studies of these, and of similar crystalline rocks in North America, in the British Islands, and in continental Europe, served in succeeding years to confirm this conclusion as to the gneiss of the Highlands, which was again asserted before the geological society of London in 1881.

Meanwhile the attention of able workers in Great Britain had been turned to this great problem in Scottish geology, beginning with Hicks in 1878, and followed by Callaway and l.apworlli, all of whom labored indcfiendently of each other, bnt with concordant results. Their separate conclusions, as announced from time lo time, bnt more ftilly in 18H3, agreed in showing that the views of Mnrchison and liis followers were altogether untenable, and in disaccoi'd with the facts of stratigraphy. Ac- cording to the resiihs of these observers, pub- lished early in 188;), there are seen in the Highland region an older granitoid or Lauren- tifin gneiss, and n younger series, consisting in large part of tender gray gneisses and granu- Utes, with mica aclasis, which are the charac- teristic rocks of the High lands, -and have been various!}' named Upper Pebidian. Grampian,
 * ind Caledonian. They are indistinguishable

from the younger gneisses of the Alps, and from the Montalban of North America, to which they were already referred in 1871. The imconforuiable superposition of the younger tipon the older gneissic series, and the fact that the Cambrian strata rest unconformably ui>on both, and are younger than either, are also shown. The existence of great parallel north and south faults, with upthraws on their east sides, bringing up suceesaively higher rocks ; the fact that these faults pass into sigmoid flexures, in which both the younger gneiss and the Cambrian rocks were involved ; and also that the younger gneiss is made to overlie the latter by dislocations, which were accompanied by a great thrust from the east, throwing both scries into a succession of folds overturned to the west, giving the whole region a general eastern dip, — were made apparent, as may be seen in the various papers of Hicks, particu- larly that in the Quarterly geological journal lor May, 1883, with appended notes by Bon-

��ncy, (m<! in the papers in the Geological maga- zine for the same year, lij- Callaway and by Lapworth, the latter entitled "I'he secret of! the Highlands,' besides a later one byCalla-- way in the same magazine for May, 1884, on*] I'rogressive metamorphism. An abstract of these results will be found in a chapter on tlia progress of geology', in the Smithsonian ivport.. for 1883.

The publication of these conclusions im- pelled the geological survey of Great Brittua to direct its attention to the region for the pur- pose of defending, if possible, the i)reviou8ly expressed opinions of the official geologists ; aud, after investigations carried on in 1883 and 1884, the conclusions of the director. A. Geikie, and of his assistants, Messra. Peadi and Ilorne, are given in Nature for Nov. 13, 1884. and reprinted in the American jovrnat of science for January, 1885. Therein, while making no special reference to the results obtained by his immediate predecessors, Getkie abandons entirely the \-iews hitherto held hy him in common with Murchison and R&inaay, and conGrms those of Hicks, Callaway, and Lapworth. lie writes that he has •'■ found the evidence altogether overwhelming against the upward succession which Murchison believed to exist in Eriboll from the base of the Silurian [Cambrian] strata into an upper conform- able scries of schists and gneisses," and adds, " that there is no longer any evidence of a regular conformable passage from fossiliferous Silurian [Cambrian] quartzites, shales, and limestones, upwards into crystalline schists, which were supposed to be metamorphic Silu- rian sediments, must be frankly admitted." The same conclusions are also reached by Geikie from the re-examinations of similar sections in llossshire, prcviouslj- described by himself in accordance with the views of Murchison. Th* preliminary rejiort of Messrs. Peach and Horae, with a general section, explains the structure in complete accoi-dance with the statements already made by late observers, as explained

Geikie. in the pnper just cited, calls attention to the laminated and schistose structure devel- oped by the great pressure and friction along the lines of movement in the displaced gneis- sic and hornblcndic rocks, and also to similar changes produced by the same agency in de- trital iixiks, such as arkosc in this region. Both of these structural alterations are np|iarently included by Geikie under the head of what he calls a ' regional mctaraoriihism.' This, how- ever, is a misapplicnlion of the terra, likely to confute .nnd mislead the reader, since local

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