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ff 



544 



UEPOUT— 1884. 



ir 



i 



Ml 



Now the Wrekiu volcanic I'ocks must bo distinctly older tlian the 

 Ordoviciixn ; henco wo refer them to the same set of outbursts as the Lite 

 Archa3an volcanoes of Wales. But there are considerable resemblantjcs 

 between these and the oldest rocks at the Lickey, Harthhill, and the 

 more rhyolitic lavas of Charnwood (not to mention resemblances of the 

 ordinary detrital beds), and all these differ markedly from the lavas of 

 the Aroni<i; or IJala beds of Wales. ]Ience it seems reasonable to sup])nso 

 that in tlie latest part of tho Arcluvan period there wave numerous 

 volcanic outbursts of very similar materials in Britain, and that of thest 

 the beds already mentioned are records. 



(C) SOOII.AND. 



(10.) The niiildamh. — This mountainous region has for full thirty 

 years been a battle-ground for rival theories, and the war which was so 

 keenly Avaged between Murchison and Nicol has now, after a truce of 

 exhaustion rather than of agreement, again broken out. In tho limited 

 space of this paper it would bo impossible to enter into tho details of the 

 controversy, so that it must .suffice to give the main outlines of the 

 chief conflicting views. First, as to tho points on which the main body 

 of competent observers arc agreed. Along the western border of the 

 N.W. Highlands and in the Outer Hebrides, is a great area of metamorphie 

 rock, which clearly forms tlic foundation-stones of tho district. This, the 

 Fundamental g*^ ?iss, Lewisian gneiss, Hebridean gneiss, &c., of difTciciit 

 authors, is cloi .-ly a series of great antiquity ; its characteristics recall 

 those of the Lower Laurentian series of America, and the most ancient 

 rocks of Scandinavia, the Alps, Bohemia, we may say of any locality in 

 the world where we seem to touch the records of the dawn of geological 

 history. Its rocks may be described in the words of Dr. A. Geikio, tho 

 present head of the Geological Survey of Great Britain : ' They consist of 

 a tough massive gneiss, usually hornblendic,' with bands of hornblende- 

 rock, hornblende-schiot, actinolite-schist, eclogite, mira-schist, sericite- 

 schist, and other crystalUne rocks. In two or throe places they enclo?e 

 bands of limestone.^ .... In traversing the western seaboard, from 

 Cape Wrath to Loch Torridon, I have ascertained that those ancienr 

 rocks are disposed in several broad anticlinal and synclinal folds, the 

 angles of dip not exceeding 30° to 40°, and the strata succeeding each 

 other with unexpected regularity, though here and there showiiig great 

 local crumpling. The lower portions of tho series are on the whole more 

 massive than the upper, and more traversed by pegmatite veins.' •' Abovr 

 this metamorphie series comes a mass of indurated reddish grit, snn:ctirae^ 

 a conglc jaerate or breccia, commonly called the Torridon sandstone. Tlii'^ 

 is of very variable thickness ; in the Loch ^Farco district it is supj)osed to 

 be 'at least 8,000 feet thick,' ' while near Loch Eriboll it is practically 

 absent. It overlies, with grcxt uiiconformitj', the Hebridean gneiss, and 

 is in turn overlain, it is generally said unconformably, by a group of 

 quartzitcs, which are succeeded conformably by calcareous beds. It i^ 

 proved, on the evidence of fossils, that these limestones and the undcrlyin':' 

 quartzitcs are of Ordovician age ; hence tho 'Torridon sandstone ' is con- 

 sidered to be Cambrian. In apparent succession to the Ordovician limo- 



' liliU'k mica also is by no iiioaiis wiintiiijj. — T. fl. 1>. 



* lliplily crystalline, so far as I know. 'I'. (!. I'.. 



' Tcvt-lnwh of (Icoliiiiij, p. (1 10, (■<!. I ssl'. ' (Ic'kii'. ;//,'(/, \<. tl.'n!. 



