HARDWICKE'S SCIENCE-GOSSIP. 



171 



as a pleasant relaxation after the active business-life 

 of the day. And to the "pleasant relaxation" of 

 similar men we cordially recommend its perusal. 



A Physical, Historical, Political, and Descriptive 

 Geography, by Keith Johnston, F.R.G.S. (London : 

 Edward Stanford). The geographical transformation 

 in the territorial divisions of Europe which has 

 taken place within the last ten years, as well as the 

 numerous discoveries in Central and Southern Africa, 

 Australia, New Guinea, &c, have almost turned our 

 antiquated geographical manuals into so much dead- 

 stock on the bookseller's shelves. A new manual was 

 sorely needed, and perhaps nobody was better fitted 

 in every way to prepare one than the unfortunate, 

 but gifted author of the present volume. His name 

 and that of his father have long been associated with 

 publications concerning physical geography ; and 

 young Keith Johnston himself revised the proofs of 

 the volume before us whilst conducting the Geogra- 

 phical Society's expedition in the exploration of the 

 country north of Lake Nyassa. There now lie his 

 bones, another victim to the brilliant fatality of 

 African travel ! In the work before us we have a 

 manual which, for scientific accuracy and the clearness 

 with which the facts are arranged, has never before 

 been equalled. And we feel certain that for many a 

 day to come it will hold its own against all comers. 



A SKETCH OF THE GEOLOGY OF 

 SWANSEA AND THE NEIGHBOURHOOD. 



By Horace B. Woodward, F.G.S., of the 

 Geological Survey of England and Wales. 



SWANSEA is situated on the southern side of 

 the great coal-field of South Wales which 

 extends from Ponty'pool in Monmouthshire to the 

 margin of St. Bride's Bay in Pembrokeshire. This is 

 the largest coal-field in England and Wales ; it 

 occupies an area of 900 square miles, and its included 

 strata have been estimated at 12,000 feet in thickness. 

 Geologically speaking the Coal-measures lie in a 

 "basin," perhaps the most uniform and well-marked 

 in the country, although its continuity is broken by 

 the bays of Swansea, Caermarthen, and St. Bride. 

 This basin is formed of the Lower Carboniferous 

 rocks and Old Red Sandstone, which make an elevated 

 boundary on its northern side, where the Old Red 

 Sandstone rises up in the Vans of Brecon to a height 

 of 2800 feet ; but the Coal-measures themselves stand 

 up in bold hills and ridges, for the most part above 

 the southern edge of the basin, which from Cardiff to 

 Bridgend has been worn away and much concealed 

 by Secondary and newer deposits. 



The immediate neighbourhood of Swansea (in- 

 cluding the peninsula of Gower, and the coast-line 

 between Kidwelly and Aberafon) is represented on the 

 Geological Survey map, sheet 37. The Survey com- 



menced its labours in this district in 1837, and the work 

 was done by Sir Henry De la Beche and Mr. (after- 

 wards Sir William) Logan. It is only just to the latter 

 to state that for several years previously he had been 

 engaged in a careful survey of the district, and that 

 with true public spirit he presented his maps to the 

 Geological Survey.* 



The rocks met with in the area embraced by sheet 

 37, and those in adjoining tracts, included within a 

 range of twenty miles from Swansea, are the following : 

 — Cambrian, Silurian, Old Red Sandstone, Carboni- 

 ferous, Triassic, Liassic, and sundry Post-Pliocene 

 deposits. 



Cambrian and Silurian. 



The north-western portion of the coal-basin is 

 bounded by the Cambrian (or Lower Silurian) and 

 the Silurian (or Upper Silurian) rocks of Caermar- 

 then, Llandeilo, and Llangadock. These include the 

 Llandeilo Flags, shales and sandstones with the 

 trilobites Ogygia Buchii, Trimiclens Jimbriatits, and 

 mollusca of the genera Lingula, Leptama, and Ortho- 

 ceras. Wenlock beds are represented by shales with 

 Orthoceras, and the trilobite Phacops ; and the 

 Ludlow beds are shown by purple grey and red 

 sandstones and conglomerate, capped by grey lami- 

 nated and micaceous sandstone (tilestone), with the 

 mollusca Athyris navicnla, Chonetes lata, &c. 



The Silurian rocks rest unconformably upon those 

 of Cambrian age, as shown near Builth ; and in that 

 neighbourhood De la Beche found it no easy task to 

 determine a boundary-line between the Ludlow rocks 

 and the Old Red Sandstone. The tilestones, which 

 formed a convenient boundary westwards, did not 

 extend so far, and he had to admit that the change 

 from Silurian conditions to those attending the de- 

 position of the Old Red Sandstone, though great, 

 was gradual.f These facts become of particular 

 interest when we turn to the alterations in opinion 

 that within the last two years have been expressed 

 concerning the Old Red Sandstone, to which 

 reference may subsequently be made. The main 

 geological features of the country around Swansea, 

 however, demand our first attention. 



Old Red Sandstone. 



The Old Red Sandstone is divided into, firstly, 

 an upper division of red sandstone and quartzose 

 conglomerate, which is developed at Llanmadoc and 

 Cefn-y-Bryn in Gower, and which forms the chief 

 heights of South Wales (the Vans or Brecknock 

 Beacons) ; and, secondly, a lower division of marls 

 with the irregular mottled calcareous beds termed 

 " cornstones," which division is not represented 



* De la Beche, " On the Formation of the Rocks of South 

 Wales and South-western England." Mem. Geol. Survey, vol. i. 



p. 145. 



t De la Beche, op. at. pp. 4S 47. 



I 2 



