l82 



NATURE 



[December 21, 1899 



Particular attention has been given to the granites of 

 Ben Cruachan and Glen Etive, and it is noted that the 

 porphyrite dykes and sills so numerous in the Cruachan 

 granite are entirely absent from the Glen Etive mass. 

 The evidence tends to show that the chronological order 

 was (i) Ben Cruachan granite, (2) Porphyrite dykes and 

 sills, and (3) Glen Etive granite and quartz-porphyry 

 dykes and sills. It is observed that the huge granitic 

 mass of Ben Cruachan affords special facilities for the 

 study of the phenomena of contact-metamorphism, of 

 which particulars are given. A careful study was made 

 of the Cordierite-bearing rocks which occur among the 

 altered sediments at the back of Loch Awe Hotel, and 

 the discovery in them of Corundum is noted and 

 discussed. 



Among the Devonian and older slaty rocks of Devon 

 and Cornwall and the associated eruptive rocks much in- 

 teresting work is in progress. 



In Carboniferous regions the chief work has been done 

 in the coal-fields of South Wales, North Staffordshire and 

 Leicestershire ; and there are some new observations on 

 the volcanic rocks in the Carboniferous Limestone of 

 Somerset. 



The changes which take place in the Carboniferous 

 Limestone series of Glamorganshire are duly noted, and 

 we have some account of the Millstone Grit and its beds 

 of "silica stone," from which the celebrated Dinas fire- 

 bricks are made. The faulted anticlinal disturbances of 

 the Vale of Neath and Cribarth are described and illus- 

 trated. A study of these disturbances is of the highest 

 practical importance, an instance being given where the 

 Pennant escarpment exhibits a gentle and uniform dip, 

 while the soft Lower Coal-measures below are thrown 

 into sharp folds. Explorations are now showing that the 

 lower measures are too much crushed and broken over 

 considerable tracts near the head of the Rhondda valleys 

 for their coals to be workable, though the Pennant rock 

 overlying them is unbroken. Reference is made to the 

 anthracitisation of the coals which proceeds from the 

 eastern side of the South Wales coal-field in a direction 

 somewhat west of north. It is remarked that the lower 

 seams of the north crop in the Vale of Swansea are true 

 anthracites, while one seam becomes a steam-coal at 

 Resolven, and is intermediate between a steam-coal and 

 an anthracite at Crynant. Of the Neath seams, one alone 

 is a house-coal, all the others being steam -coals, although 

 they correspond to the Llantwit group, the most noted 

 house-coals of the coal-field. No connection has been 

 traced between the anthracitisation and the faulting of 

 the district, but the change seems rather to be a form of 

 regional metamorphism dependent upon the temperature 

 to which any part of the coal-field has been subjected 

 during depression, as was suggested many years ago by 

 De la Beche. The results of further investigations on 

 this subject will be looked for with interest, for although 

 much has been done by local observers, the question can 

 only be solved by patient detailed and continuous map- 

 ping, and the tabulating of evidence over a large area. 



In the North Staffordshire coal-field much has been 

 done to determine and map in detail the main sub- 

 divisions of the Coal-measures. The uppermost division, 

 known as the Keele series, comprises a considerable 

 thickness of red sandstones, marls, and occasional bands 

 of cornstone — beds formerly regarded as Permian, but 

 now recognised to be strictly conformable to the Upper 

 Coal-measures. Some of the red marls in this series 

 contain plants of Coal-measure species, and it is re- 

 marked that the division cannot be classed with the 

 Permian formation of Lancashire and the north-eastern 

 counties. It remains to be proved how far it corre- 

 sponds with the Supra-Carboniferous or Permo-Carbon- 

 iferous division which is engaging much attention on the 

 continent and in other regions abroad. It is remarked 

 that the determination of the horizons in the Coal- 

 NO. 1573, VOL. 61] 



measures may prove to have an important industrial 

 and commercial bearing. The fact that the limestone- 

 bands of Newcastle-under-Lyme lie at the base of a 

 group of grey Coal-measures, intercalated between an 

 upper group of red strata (Keele Series) and a lower 

 group of red strata (Etruria Marls), has enabled the 

 survey to detect true Upper Coal-measures in Keele 

 Park, Shutlanehead, and to the west of Leycett ; and 

 there seems to be little doubt that the Coal-measures of 

 the Pottery Coal-field lie not far from the surface under 

 Little Madeley and Craddocks Moss. Evidence has 

 been obtained that the strata on the north-west side of 

 the North Staffordshire anticline do not uninterruptedly 

 descend beneath red rocks (so-called Permian) to the 

 west of Leycett, but rise locally westward under Hayes. 

 The effect of this change of inclination is to bring to the 

 surface strata which lie considerably below the un- 

 productive red series, and to bring the prmcipal coals 

 and ironstones within reach further west than might 

 have been expected. Iron-ore has been discovered in 

 the Fenton Park Clay-pits. It is a sphero-siderite 

 yielding 387 per cent, of metallic iron. This may prove 

 to be of considerable importance. 



A small patch of Carboniferous rocks has been deter- 

 mined at the Bridge of Awe, in the Lome area, a fact 

 interesting in connection with the discovery, made many 

 years ago by Prof. Judd, of Carboniferous rocks on the 

 east shore of the Sound of Mull, near Ardtornish. 

 Further evidence of Lower Carboniferous rocks in Arran 

 has also been obtained. 



Brief observations on Permian rocks in Leicestershire 

 and in Arran are recorded, and there are fuller notes on 

 the Trias (including the Rh^etic Beds) in South Wales, 

 and on the Trias of the Midland Counties and Skye. 

 Short notes again are given on the Lias of Glamorgan- 

 shire, but the only reference to the Oolites is in a note of 

 a deep boring (439 feet) at Oxford. We hope to hear 

 more of this bonng, as it is stated to pass from Inferior 

 Oolite into Lower Lias with no evidence of Upper and 

 Middle Lias, which outcrop at Pawler, near Woodstock. 

 The Cretaceous rocks have received attention in the 

 southern and eastern counties. There are notes on 

 Chalk inliers which form remarkably bold features in the 

 neighbourhood of Cranborne Chase. There are detailed 

 accounts of the Lower Greensand series of Norfolk, but 

 these facts, which convey much new information, have 

 now been printed in full in the Geological Survey 

 memoir on " The Geology of the borders of the Wash." 

 It is mentioned that the name Selbornian, from Selborne 

 in Hampshire, is proposed as a term for the Gault and 

 Upper Greensand, formations which have long been 

 held to be portions of one stage, although it is useful and 

 necessary on geological maps to separate the clayey 

 Gault from the sandy Upper Greensand. The Selbornian 

 stage will include the Red Chalk of Norfolk, Lincoln- 

 shire and Yorkshire, as well as the Gault, and the sands 

 Malmstone and Chert-beds of the Upper Greensand. 

 Where fully developed it' is divisible into four pala^onto- 

 logical zones, in descending order : (4) zone of Pecfen 

 nsper (as usually known), which would more conveniently 

 be called the zone of Holaster fossaiiusj (3) zone of 

 Ammonites rostraius, with its local sub-zone of A^ 

 varicosus J (2) zone characterised by Ammonites lautus, 

 A. denarius, and A. interruptusj (i) the zone of 

 A mmonites mammillatus. 



The observations on Tertiary strata refer to Bagshot 

 Beds, and to records of new wells at Mundesley and 

 North Walsham which passed through Pliocene strata 

 as well as Glacial Drift. More important are the re- 

 searches on the volcanic rocks of Skye, which tell of the 

 numerous sills of basalt and diabase which have been 

 intruded into the basaltic lavas. Though the lavas are 

 older, these sills are younger than any of the great plu- 

 tonic intrusions of gabbro and granophyre. Reference 



