200 



HARDWICKE'S SCIENCE-GOSSIP. 



Submerged Forest and Raised Beaches.— In 1859 

 Mr. M. Moggridge described a submerged forest 

 which was exposed in the excavation of the Swansea 

 Docks. Beneath a deposit of made ground, sand, 

 and loose gravel (varying from 6 to 20 feet in thick- 

 ness), he recorded three beds of peat containing 

 leaves, trees, &c, which alternated with blue marine 

 clay to a depth of over 18 feet. The clay contained 

 Scrobicularia pipcrata. In the peat he noticed re- 

 mains of oak, beech, birch, alder, hazel, and crab- 

 tree ; and he observed that in very many cases roots, 

 still attached to plants in the peat, descended into the 

 clay beneath. 



Mr. Moggridge noticed also the occurrence of a 

 raised beach to the west of the Mumbles ; * while 

 Professor Frestwich has recorded one that was to be 

 seen for a mile along Mewslade Bay, westward of 



Paviland.f 



These changes of level bear out what is indicated 

 by the Gower Caves, when what is now the Bristol 

 Channel was probably an open plain "supporting 

 herds of reindeer, horses, and bisons, many elephants 

 and rhinoceroses, and now and then being traversed 

 by a stray hippopotamus, which would afford abun- 

 dant prey to the lions, bears, and hyaenas inhabiting 

 all the accessible caves, as well as to their great 

 enemy and destroyer man." % 



Dr. Falconer considered that the Gower Caves 

 were fdled with the mammalian remains after the 

 deposition of the boulder-clay before mentioned. 



Recent Deposits. — Since this period, submergence 

 has allowed the sea to enroach over much of the area 

 it now occupies, while it has eaten its way through 

 the softer rocks into the bays of Caermarthen, 

 Oxwich, and Swansea, that are hollowed out of the 

 Coal-measures. As the sea encroaches, so flats occu- 

 pied by sand mark its progress. 



On this coast the south-west winds are particularly 

 felt : the bent trees at Dunraven, and many other 

 places becoming conspicuous indications of it. The 

 wind, however, has made great efforts to restore to 

 the land some part of the material it has lost, to 

 which the numerous burrows of Blown sand testify. 

 At Candleston Castle great hills of sand rise up 

 against the Carboniferous Limestone, forming Newton 

 Burrows which stretch away to Forth Cawl. Like- 

 wise at Kenfig, Margam, and Aberafon, at Crymlyn, 

 Penard, Penmaen, Oxwich and Hill End, at 

 Llangenydd and White ford, are these hills of Blown 

 sand to be found. 



Alluvial flats border the Tawe, the Neath, and the 

 Llwchvvr ; and tracks of marsh and moor occur at 

 Aberafon, Margam, Llanrhidian, and Oxwich. 



Eastwards, alluvial tracts spread out here and 

 there like lakes, as at Pen Coed, Penlline Moor, and 



* Quart. Journ. Geol. Soc. vol. xii. p. 169. 



t 1'iid. vol. xvi. 



\ See Dawkins, " Cave Hunting," p. 290. 



Morfa Ystrad Owen. West of Llantrissant, Gwaun 

 Ynysplwm might even be taken for an old glacier- 

 dammed pool, for it is almost hemmed in on the 

 south by a bank of drift-gravel which the railway 

 cuts through. 



Having thus indicated the leading features in the 

 geology of the country around Swansea, mention may 

 be made in conclusion of some of the larger questions 

 concerning the classification of the rocks which are 

 now undergoing consideration. 



The proximity of the South Wales coal-basin to 

 the disputed rocks of the Devonian area has naturally 

 led to several attempts at correlating the beds in the 

 two districts. It is now known, through the labours 

 of Professor A. Geikie, that the Old Red Sandstone 

 of Scotland consists of two great divisions, a lower 

 one passing down conformably into the Silurian 

 shales, and an upper one graduating into the lower 

 Carboniferous rocks above, with a complete discord- 

 ance between these two divisions. The same 

 arrangement has been described by Mr. Kinahan and 

 Professor Hull, in the south-west of Ireland, where 

 the Dingle or Glengariff grits, which in lithological 

 characters seem to belong to the Old Red Sandstone, 

 pass downwards into the Silurian rocks, and are over- 

 laid discordantly by beds of true Old Red Sandstone. 

 Not enough is known of the precise relations of the 

 two divisions of the Old Red Sandstone in the counties 

 of Brecknock, Hereford and Monmouth. They have 

 usually been considered as conformable, and the 

 entire series in the neighbourhood of Cardiff has 

 recently been stated to be a continuous deposit, from 

 the conformable Silurian at its base to the conform- 

 able Carboniferous at its summit.* There is there- 

 fore no positive evidence of a break between the Old 

 Red Conglomerate and the " Cornstone series ; " the 

 former of which Professor Hull regards as the 

 equivalent of the Pickwell Down Sandstone of Devon- 

 shire ; the latter, he regards as representing the so- 

 called Middle Devonian, and the Lower Devonian 

 beds above the Foreland Group.f 



In proceeding westwards trom Llandeilo, it has 

 been pointed out by De la Beche that the Old Red 

 Sandstone begins to overlap the Silurian rocks and to 

 rest directly upon the older strata. Still further the 

 Old Red Sandstone is overlapped by the Carboniferous 

 Limestone, which again near Haverfordwest is over- 

 lapped by the Coal-measures, the latter thus resting 

 in that neighbourhood on the Cambrian rocks.J 

 Owing to this overlap of the Old Red Sandstone, the 

 passage-beds are hidden, but Professor Hull thinks 

 that " the purple and reddish sandstones, shales, and 

 conglomerates of the Ridge of the Trichrag, under- 



* W. J- Sollas, Quart. Journ. Geol. Soc. vol. xx.w. p. 494- 

 t Geol. Mag. Decade II. vol. vi. p. 192, and Quart, journ. 

 Geol. Soc. vol. xxxvi. p. 269. 



X Mem. Geol. Survey, vol. i. p. 24- 



