October 17, 1912] 



NATURE 



209 



distinguished by lit-par-Jit intrusions. . The granite 

 material in these cases formed minute sills parallel to 

 the foliation of the associated gneiss into which it had 

 been intruded. The granite rises as a d3ke and the 

 sills diminish in thickness and extent as they near 

 the surface. In the interior parts the granite is 

 usually grey and contains more biotite than muscovite, 

 and oligoclase is usually abundant. The oligoclase 

 and biotite are found to diminish steadily as the rock 

 is traced towards the taper end of the sills. At this 

 point there is little oligoclase and often no biotite ; 

 muscovite is fairly common and the bulk of the felspar 

 is of alkaline composition. It would appear that the 

 fissures in which the dykes occur were filled with 

 igneous material, and that under great pressure the 

 walls were burst open and the still liquid material 

 forced out, and thus separated from that which had 

 already become segregated. This phenomenon may 

 be described as magmatic differentiation intensified 

 by dynamic action. Mr. Barrow also read a paper 

 on buckled folding. Descriptions have been pub- 

 lished of areas of regional crystalline metamorphism 

 in which the dip of the bedding is described as at a 

 low angle over a considerable area. Experience is 

 gradually proving that these altered sediments are 

 always intensely folded, and the low dips really repre- 

 sent the most complicated structure, for which the 

 name " Buckled Folding " is suggested. This structure 

 is best seen in the Moine Gneisses, and its development 

 can be studied in the cliff sections between Stonehaven 

 and Muchalls. The grits and shales on the limb of 

 the folds, near Stonehaven, ascend the cliffs in an 

 unbroken course from bottom to top, being isoclinal 

 and unbent. But as we proceed northwards the course 

 of the grit bands up the cliff face is no longer straight, 

 but a small overfold, or " buckle," is developed in it. 

 At first only one is seen in the whole height of the 

 cliff, then two, then three, and so on, until they 

 are so close together that the still straight portion of 

 the fold is no longer than the "buckled" or over- 

 folded portion. If the upward course of each grit 

 band be followed, it will be found that this structure 

 does not alter the dip of the band as a whole. It still 

 descends at much the same angle, but by a zigzag 

 course. The overfolds all face in the same direction 

 right up to Muchalls, and must have been produced 

 after the isoclinal folding was completed. There is 

 no justification for separating the buckled beds from 

 those in which buckling does not occur. A key to 

 the connection is found in the area about Shiehallion, 

 where the quartzose beds forming the margin of the 

 quartzite and containing the boulder bed and the lime- 

 stone show isoclinal folding ; whereas further north 

 the same group comes on again, but this time with 

 buckled folding, or Moine gneiss. 



Dr. B. N. Peach and Dr. J. Home described some 

 interesting investigations which they had recently made 

 on the Archaean rocks of Lewis, in which they showed 

 how closely these beds corresponded to the rocks of 

 the adjoining mainland, without the great series of 

 acid intrusions. The structure is coarsely granulitic, 

 and there is a marked absence of the pyroxene-gneisses 

 with blue quartz, of pyroxene-granulites, and other 

 basic forms, which are so characteristic of the main- 

 land. The remarkable series of basic dykes in the 

 west of Sutherland had not been detected in Lewis. 

 The north-west and south-east strike, referred to by 

 Murchison, was not characteristic of the gneisses of 

 Lewis. The dominant strike is almost north and south, 

 but north-east to south-west or east to west in other 

 areas. The flaggy granulitic gneisses of the Butt of 

 Lewis, which appear to run southwards along the belt 

 of high ground between Stornoway and Barvas, 

 resemble closely the Moine gneisses east of the Moine 

 thrust-plane, but they differ petrologically from the 



NO. 2242, VOL. go] 



rocks of sedimentary origin which form the Moine 

 series. The system of overfolding and the direction of 

 the axial planes of the folds appro.ximate to those found 

 in the Moine rocks on the mainland. The platy rocks, 

 or mylonites, occur along definite lines of movement 

 approximately north to south, and thrust-planes have 

 been detected which point to displacement in a westerly 

 direction. Various stages in the development of my- 

 lonites from the acid and basic gneisses are repre- 

 sented. In the discussion which followed the value 

 of these investigations was emphasised by Dr. Flett 

 and others. 



Important discoveries of fossils in old rocks 

 were announced by Dr. R. Campbell (Edin- 

 burgh) and Prof. T. J. Jehu (St. Andrew's). Dr. 

 Campbell described fossil remains found in the Jasper 

 and Green Schist series of the Highland border, at 

 Craigeven Bay, Stonehaven. Crushed spilitic lavas 

 with intercalated black shales, jaspers, and cherts, 

 which in their lithological characters resemble closely 

 the green igneous rocks and associated sediments along 

 the line of the Highland fault, appear on the old 

 Geological Survey maps as of (?) Arenig age. In 

 1909, in company with Dr. Peach and l3r. W. T. 

 Gordon, the author found several fossils in the black 

 shales. Detailed search by Mr. D. Tait revealed 

 fossils of the forms Lingulella, Obolella, Acrotreta, 

 Linnarssonia, and Siphonotreta ; a bivalve phyllocarid 

 allied to Caryocaris and Lingulocaris ; and cases of a 

 tubuloid worm. The above genera are most commonly 

 found in the Ordovician beds and in the L'pper Cam- 

 brian, but, owing to the absence of graptolites. Dr. 

 Peach suggested that Upper Cambrian w-as the most 

 probable age. Whatever may be the ultimate decision 

 as to their stratigraphical horizon, the discovery of 

 these fossils leaves very little doubt that the boundary 

 fault series is not pre-Cambrian. 



Dr. Jehu followed this paper by one on the dis- 

 coverv of fossils in the boundary-fault series, near 

 .Vberfoyle. This series is well exposed between Loch 

 Lomond and Callendar, forming a narrow belt 

 separated by a reversed fault from the Lower Old Red 

 Sandstone on the south-east, and probably by a line 

 of thrust from the Leny Grits on the north-west. It 

 consists of black and grey shales, cherts, grits, and 

 calcareous beds. Remains of Radiolaria were dis- 

 covered by Dr. Peach some years ago in cherts near 

 Gualann. Recently a number of fossils have been 

 found in pale-grev chert bands near Arndrum. These 

 fossils occur in muddy films in the chert belt. They 

 are almost all hingeless brachiopods, and the follow- 

 ing forms have been determined by Dr. Peach : — - 

 Acrotreta, Lingulella, Obolus, Obolella; also the flat- 

 tened chaetsB of polychaete worms. These fossils were 

 regarded as indicating an Upper Cambrian age. Dr. 

 Home, in the discussion, regarded the collection of 

 fossils from the chert and green-schist series at Stone- 

 haven and Aberfovle as the most important palasonto- 

 logical "find" affecting Highland geology since the 

 discovery of Olenellus in the west of Ross-shire. The 

 strata containing these fossils, which had been pro- 

 visionally referred to the Upper Cambrian by Dr. 

 Peach and Dr. Walcott; could no longer be considered 

 as of pre-Cambrian age, like those of similar rocks in 

 Anglesey. At a subsequent meeting Dr. Home read 

 a letter from Dr. Ami (Toronto), who had examined 

 Dr. Jehu's collection of fossils from Aberfovle, and 

 found them closely resembling those obtained from 

 Upper Cambrian beds belonging to the Quebec group. 

 His opinion was based partly on the brachiopods and 

 partly on the occurrence of an obscurely preserved 

 graptolite resembling Retiolites ensiformis. Hall — a 

 tvpe eminently characteristic of the Sillery Sandstones 

 of the Quebec group of Upper Cambrian age. Dr. 

 Home further stated that this form had been shown 



