i74 



HARDWICKE'S SCIENCE-GOSSIP. 



It consists of a conglomerate containing pebbles of 

 coal, sometimes 4 inches in diameter, pebbles of 

 ironstone, and boulders of granite and mica-slate, 

 these latter very rarely. The presence of this bed 

 indicates that the Lower Coal-measures must have 

 been (at any rate locally) consolidated and upheaved 

 prior to the accumulation of the Pennant Grit ; a 

 disturbance which might perhaps have had something 

 to do with the production of the anthracite. Pebbles 

 of anthracite have also been noticed in the Pennant 

 Grit and Upper Coal-measures of the Bristol coal- 

 field, where the coals above the Pennant Grit were 

 bituminous, and those below it, anthracitic* 



The Pennant Grit forms, as a rule, a marked 

 escarpment or range of hills above the Lower Coal- 

 measures, from the Garth Hill (1650 feet in height), 

 near Cardiff, by Llantrissant and Margam to the 

 neighbourhood of Aberafon, and thence by Neath 

 and Swansea to Mynydd Penbre. North of the coal- 

 basin the Pennant Grit is conspicuous near Aberdare 

 and Merthyr Tydfil. 



The Upper Coal-measures comprise about 3000 feet 

 of shales, sandstones, seams of bituminous coal, and 

 underclay. They occupy large outlying masses in 

 the centre of the trough, and may be seen at Mynydd 

 Drumau and Mynydd March Howel. Near the 

 upper part are the beds developed at Penllergare, 

 north of Swansea, and those of Llanelly, which 

 latter appear to constitute the highest beds in the 

 coal-field. Although these names were employed 

 by De la Beche to denote the uppermost beds of the 

 Coal-measures, there is nothing distinctive about 

 them. The seams of coal vary from one to seven 

 feet in thickness. 



Throughout the coal-field, indeed, the seams are 

 very variable, and there is no evidence to show that 

 any one bed of coal has been continuous over the 

 whole South Wales coal-field ; nor are the thickest 

 seams spread over the widest areas. 



When the Geological Survey commenced its labours 

 in the Swansea district, Logan pointed out to De la 

 Beche the constant occurrence of the underclay, 

 penetrated by roots of Stigmaria, beneath each seam of 

 coal.f These beds of underclay (known also as Bottom- 

 stone, Pouncin, &c.) are generally of an argillaceous 

 character, yielding a good fireclay (one capable of 

 being made into bricks which stand the fire of a 

 furnace), and they vary from a few inches to more 

 than 10 feet in thickness. Sometimes, however, 

 they become sandy, and two highly siliceous varieties 

 are mentioned by De la Beche as occurring on the 

 sea-shore near Lilyput, between Swansea and the 

 Mumbles. The interesting point in connection with 

 these beds of underclay, is the fact that they were 

 evidently the ancient soils upon which grew the vege- 

 tation that gave rise to each overlying seam of coal. 



* See Geol. Mag. vol. ii. p. 134. 



t See Logan, Trans. Geol. Soc. 2nd series, vol. vi. p. 491. 



At Cwm Llech, towards the head of the Swansea 

 valley, a group of Sigillaria? was formerly noticed by 

 Logan in a ravine, one of whose stems rose to the 

 height of 13 feet ; they were imbedded in the strata 

 in the position in which they grew, and the largest 

 stem was 5 feet 6 inches in circumference.* 



Besides several species of Sigillaria, Lepidoden- 

 dron and other forms have been met with in the Coal- 

 measures. Of mollusca species of Nautilus, Gonia- 

 tites, Spirifer, Modiola, and Pecten have been re- 

 corded chiefly from the iron-stones ; and Anthracosia 

 from the Upper Coal-measures. Specimens of the 

 annelide Spirorbis, and fishes of the genera Rhizodus, 

 Megalichthys, &c, were also obtained by Dr. G. P. 

 Bevan.f 



(To be continued.) 



SOME COMMON WADING-BIRDS. 



By P. QuiN Keegan, LL.D. 



{Continued from page 153.] 



ASSOCIATED with the heron, but infinitely more 

 active, vivacious, and agile, more graceful, 

 though more shy and keen-witted, is the ever beauti- 

 ful and interesting curlew (JVumeuius arguatits). The 

 exquisite spectacle of a band of these birds flying in 

 lengthy wedge-shaped rank and file from their retiring 

 grounds of the flow to their feeding quarters of the 

 ebb tide, cannot fail to impress the most heedless and 

 superficial visitor to the seashore. Their flight is 

 singularly smart, vigorous, and rapid. Immediately 

 prior to alighting on the ground, they execute in the 

 air with wings outspread yet motionless a long, closing 

 skim of inimitable grace. While wandering over the 

 tide-abandoned sandbanks, they search for shellfish, 

 &c, with unwearied assiduity and an unappeasable 

 appetite, ever probing their long, uncurved bills into 

 the slimy mud or sand, but all the while keeping a 

 sharp look-out to leeward for the advent of anything 

 suspicious or dangerous. In this exercise of vigilance, 

 however, they seem to exhibit an instinctive discrimi- 

 nation touching the actual quality or nature of the 

 source of danger. Thus, for instance, an equestrian is 

 less dreaded than a pedestrian ; places are frequented 

 at night or in early morning that would be shunned 

 during the day ; and often have we seen them feeding 

 within a few yards of some poor harmless lighter- 

 workers and mussel-gatherers, too indigent to pur- 

 chase a gun, and too kind-hearted, it is to be hoped, 

 to wantonly destroy seafowl. Sometimes we have 

 noted when a shot was fired at some distance, but 

 not at them, the birds momentarily upraised their 

 wings as if for instant flight, but then, evidently aware 



* De la Beche, Mem. Geol. Survey, vol. i. p. 183. 

 t Iron Ores of Great Britain, part 3; Bevan, "Geologist," 

 vol. i. p. 505. 



