November 7, 1895] 



NATURE 



21 



the Loch Maree district. It is thus shown that the " Fucoid 

 beds " contain the fossils of the Oknellus-zone from the River 

 Carron in Ross-shire to Loch Assynt in Sutherland. 



An important addition to the evidence that tends to connect 

 the quartzites and their associated strata of the south-western 

 Highlands with those of Sutherland and Ross, has been obtained 

 in tiie island of Islay. Reference was made in the last Report 

 to the occurrence of worm-tracks in the dolomitic shales of that 

 district which so greatly resemble the characteristic "Fucoid 

 beds" of the north-west Highlands. Twenty specimens of 

 tracks and burrows from the Islay shales have been obtained by 

 Mr. Macconochie, and perhaps it is not too much to hope that 

 eventually some of the other more distinctive fossils of the 

 OieueNus-zone may yet be detected there. 



In further prosecution of his mapping of the ground between 

 l.och Carron and Loch Alsh, Mr. Peach has obtained addi- 

 tional confirmatory evidence of the view expressed in the last 

 Report that the " Moine-schists" of that region are mainly 

 altered Torridon sandstone and shale. These strata and their 

 floor of Lewisian gneiss, which is occasionally brought up along 

 sharp folds to the surface, are increasingly metamorphosed as 

 they pass to the eastward. 



Not less suggestive is the evidence recently obtained by Mr. 

 Home during his survey of the mountainous ground between 

 tlie head of Loch Carron and Loch Maree. To the east of the 

 great line of dislocation known as the (Men Logan or Kishorn 

 thrust-plane, as in the ground south of Loch Carron, lenticles 

 of Lewisian gneiss, brought up on the axes of isoclinal folds, 

 occur among the Torridonian rocks, the whole series dipping in 

 an easterly direction. That these long narrow exposures of 

 gneiss are part of the actual floor on which the sedimentary 

 formations rest, is proved by the occurrence of the basal Torri- 

 donian epidotic grits resting upon them. By means of this 

 readily recognisable zone of grits and the shaly group that over- 

 lies them, it is not difficult to map out each separate isocline and 

 to follow both the succession of the rocks and the structure of 

 the ground. 



As we advance eastwards, this metamorphism becomes more 

 marked, the peculiar type or structure of the Moine or eastern 

 schists coming out more and more clearly. It is difficult to 

 understand that any other explanation of the sections can be 

 adopted than that which obviously presents itself on the ground, 

 namely that rocks having every character of true Moine schists, 

 have here been produced by the alteration of a portion of the 

 lowest Torridonian grits and shales with infolded cores of 

 Lewisian gneiss. 



Mr. Hinxman, working in that part of Strathspey which 

 embraces the districts of Rothiemurchus, Abernethy and the 

 ground between the Spey and the Dulnan, west from Aviemore, 

 has met with a large tract of biotite-granite, similar to that of 

 the Cairn-Gorm range, to which he proposes to give the name 

 of Monadhliath granite, since it forms the eastern border of the 

 Monadhliath mountains. He has ascertained that in this 

 area, though the granite is fringed with abundant apo- 

 physes which penetrate the gneiss to distances varying from 

 a few feet to 300 yards, no fine-grained edges indica- 

 tive of the chilling of the intruded granite are to be seen. 

 The injections of eruptive material have usually taken place 

 along the planes of foliation, and the bands or planes of 

 granite tend to branch out into mere strings. Besides the 

 apophyses that can actually be traced into the main body of 

 granite, many sills, bands or lenticular veins of similar material, 

 may be seen in the gneiss immediately around the granite, and 

 doubtless emanating from it. All the granitic bands, sills or 

 \ tins, whether visibly proceeding from the granite mass or not, 

 are thoroughly granitoid in texture and sometimes markedly 

 pegmatitic. Not only do they present no chilled margins, but 

 their crystals may be seen to interlock with those of the sur- 

 K landing schists. Hence in this area there appears to be no 

 I'ion to doubt that the present crystalline condition of the 

 1 lists is coeval with the crystallisation of the material of the 

 imite veins. The evidence, so far as it has at present been 

 roUected, appears to point to two conclusions. First, that the 

 1,'ranites of Cairn-Gorm, Monadhliath, and other parts of 

 Strathspey, together with most, if not all, of the sills and veins 

 I if granite and pegmatite in that region, belong to the same 

 K'ranitic protrusion and are derived from the same magma. 

 Second, that this granitic magma has been protruded into a series 

 of holrxrrystalline schists and quartzites, and that the contact 

 metamorphism thereby superinduced, gave rise to the highly 



NO. 1358, VOL. 53] 



granulitic biotite-gneiss with bands of quartzite, which now 

 forms the prevalent rock of the whole region. 



In Deeside, Mr. Barrow has ascertained that the great granitic 

 mass south of Banchory presents a very different character. The 

 granite becomes rapidly finer in grain towards its margin, where 

 it assumes the compact texture characteristic of a granite injected 

 among already cooled rocks, while its apophyses are finer in 

 grain than the main body of the rock. Of older date than this 

 eruption is the granitic material, composed of microcline, quartz, 

 and brown mica, which in a vast number of narrow dykes or 

 veins traverses the highly crystalline schists of the south side of 

 the Dee. 



The age of the red sandstones which extend along the eastern 

 shore of Arran from Corrie to Brodick and thence across the 

 southern half of the island, underneath the various sheets of 

 eruptive rocks, has been much discussed. By Sedgwick and 

 Murchison these strata were classed as New Red Sandstone, a 

 view that was subsequently adopted also by Rainsay. After- 

 wards, however, Bryce and other writers placed them in the 

 Carboniferous system, and correlated them with the red sand- 

 stones of the north of Ayrshire and Renfrewshire. A re-examin- 

 ation of the ground was made last spring by the Director General 

 in company with Mr. Peach and Mr. Gunn. They found that 

 pebbles of the Carboniferous limestone with its characteristic 

 fossils actually occur in the breccias at the base of these red 

 sandstones between Corrie and the north end of Arran, as was 

 first observed some years ago by Mr. James Thomson. Closer 

 inspection of the coast-sections and of the interior showed 

 that, besides this evidence of a decided stratigraphical break, 

 the red sandstone, conglomerates and breccias lie unconformably 

 on the Carboniferous formations, though at the actual junctions 

 the two series seem almost conformable. That they are prob- 

 ably Permian may be inferred on two grounds. In the first 

 place, the lower group of false-bedded brick-red sandstones 

 presents the closest resemblance to the red sandstones which, 

 within sight on the opposite mainland of Ayrshire, rest upon the 

 Coal-measures, and have been referred to the Permian period. 

 In like manner, they resemble the red sandstones of the south of 

 Ayrshire, Wigtonshire, and Dumfries-shire, which are also 

 assigned to the same period. In the second place, the Arran 

 red sandstones have been found by Mr. Gunn to enclose a 

 contemporaneous volcanic group, a feature which is specially 

 characteristic of the Permian series of the centre of Ayrshire, 

 and of Nithsdale. The occurrence of Stigtnaria in the volcanic 

 series which lies some hundreds of feet above the base of the red 

 sandstones seems to remove these strata from the New Red 

 Sandstone or Trias, while the strong lithological resemblance 

 which, both as regards their sedimentary and volcanic com- 

 ponents, they present to the Permian series of the main- 

 land opposite, renders it highly probable that they are 

 Permian. 



Mr. Woodward has mapped separately in Skye, as he did in 

 Raasay, the passage-beds between the Upper Lias and the 

 Inferior Oolite, which include shaly layers, and bands and con- 

 cretionary masses of calcareous sandstone. These strata in 

 Raasay yielded Ammonites variabilis ; while in Skye they have 

 afforded a form identified by Messrs. Sharman and Newton as 

 Ammonites Siemensi, indicative of the zone of A. jurensis. 

 A. Murchisonts occurs in the lower part of the Inferior Oolite, 

 and many examples of A. humphriesianus, and other fossils, not 

 yet determined, have been obtained from the fine cliffs between 

 Bearreraig Bay and Invertote. The upper portion of the 

 Inferior Oolite does not appear to be fossiliferous on this Skye 

 coast. It contains some shaly, and lignitic bands, and concre- 

 tionary masses of sandstone, differing to some extent from the 

 mass of white sandstones so prominent on this platform in the 

 eastern cliffs of Raasay. 



The Tertiary dykes of Skye are now being mapped, both on the 

 north-east and south-east coasts. In the latter area Mr. Clough 

 finds them to vary petrographically between the two extremes of 

 pitchstone on the one side and troctolite on the other. Those 

 of acid or intermediate character on the coast north of Loch-na- 

 Daal often indicate the direction of flow of the molten rock in 

 the fissure, by the elongation of the amygdales and the orienta- 

 tion of the rows of spherulites. From the variation in the 

 positions of these structural lines, it is clear that the movement 

 of the lava was by no means always vertical, but was often 

 approximately horizontal or oscillating between the two direc- 

 tions. Records of the variations observed are being kept by 

 Mr. Clough. 



