172 



HARDWICKE'S SCIENCE-GOSSIP. 



on the south side of the coal-basin, but forms the 

 lower and more cultivated lands on the north. 

 There the cornstones are generally marked by 

 quarries, as they are used for road-metal, and burnt 

 for lime. Specimens of the fishes Holoptychius and 

 Pterichthys have been met with in the upper division, 

 but not, I believe, in the neighbourhood of Swansea ; 

 the lower division, in which fossils are more abundant 

 in the cornstones, has yielded specimens of the fishes 

 Pteraspis and Cephalaspis, and also of the crustacean 

 Pterygotus. 



The total thickness of the Old Red Sandstone is 

 estimated at about 5500 feet, of which about 4000 

 feet belong to the upper division. 



Carboniferous. 



Lower Limestone Shale. — The Lower or Carbon- 

 iferous Limestone Shale forms a connecting link 

 between the Old Red Sandstone and the Carbon- 

 iferous Limestone, consisting of arenaceous shalewith 

 occasional beds of sandstone near its base, and of 



Near Oystermouth Castle the upper beds consist of a 

 few feet of dark-coloured carbonaceous limestone in- 

 termingled with siliceous matter, and in places highly 

 fossiliferous. This bed, described by De la Beche, is 

 said to occur here and there along the boundary of 

 the Carboniferous Limestone between Swansea and 

 Caermarthen bays. 



The thickness of the limestone is estimated at 

 upwards of 2000 feet in Caldy Island ; while near 

 Llangadock, on the north side of the coal-basin, it 

 becomes reduced to 510 feet. 



Among the fossils recorded from the district are 

 remains of fishes ; mollusca of the genera Chonetes, 

 Spirifer, Productus, Orthis, Retzia ; polyzoa of the 

 genus Ceriopora, the crinoid Actinocrinus, &c. 



Here and there traces of galena have been met 

 with in the limestone, and there are "Old lead 

 works " between Llangan and Penlline, about four 

 miles south-east of Bridgend. 



Go~cver Series.- — Immediately above the Carbon- 

 iferous Limestone of Gower, at Penrice, and between 

 Llanrhidian and Oystermouth, the place of the Mill- 



Fig. 94. — Section of the southern side of the South Wales coal-basin, near Swansea. (after Sir W. E. Logan). Scale 1 inch to 2 miles. 

 S. Newton, near Town Hill, Bryn Near N 



Sea. 



Newton, near 

 Oystermouth. 



Town Hill, 



near Swansea 



[570/eet). 



Bryn 

 Dafydd. 



Near 

 Ce/n Dritn. 



Old Red Sandstone. 



2. Lower Limestone Shale. 3. Carboniferous Limestone. 4. Gower Series. 

 6. Pennant Grit. 7. Upper Coal-measures. 



5. Lower Coal-measures. 



shale interspersed with nodular beds cf limestone 

 towards the top. The gradual change is well 

 exhibited in a section drawn many years ago at 

 Skrinkle Haven, near Tenby, by Professor Ramsay.* 

 The sections at Caldy Island also show it.t In 

 Pembrokeshire the thickness of the beds is estimated 

 at nearly 600 feet. In some parts of the district they 

 are not represented on the Survey maps, on account 

 of their diminished thickness, nevertheless traces of 

 them are usually to be detected around the borders 

 of the Old Red Sandstone in the peninsula of 

 Gower. Encrinites, and species of the mollusca 

 Bellerophon and Rhynchonella, have been recorded 

 from the district. 



Carboniferous Limestone. — The Carboniferous or 

 Mountain Limestone consists for the most part of 

 grey and bluish-grey limestone and encrinital marble ; 

 broken encrinites being more abundant in the lower 

 portion, corals in the upper. It forms the main 

 portion of Gower, from the Mumbles to Worm's 

 Head, where it is from 1200 to 1500 feet in thickness. 

 At the latter place it is much disturbed and faulted. 



* De la F.eche, op. cit. pp. 108, no. 



t Salter, " On the Upper Old Red Sandstone and Upper 

 Devonian Rocks." Quart. Journ. Geol. Soc. vol. xix. p. 476. 



stone Grit is occupied by a series of "black shales 

 mingled with sandstones," to which the name Gower 

 series has been applied (see section). According to 

 De la Beche they appear to form a lenticular mass 

 interposed between the Coal-measures and the Car- 

 boniferous Limestone, rendering it difficult to draw 

 fine lines of distinction between them. 



The following section is abbreviated from one he 

 recorded as taken along the course of the stream 

 near Bishopston : — 



Black shale with here and there thin bands Feet in. 



of sandstone and limestone 797 10 



jGrey sandstones and black shale .... 12 o 



Gower I Black shale with nodules of ironstone, &c. . 527 o 



series. \F"ine-grained sandstone 75 o 



Black and grey flinty slate and shale, contain- 

 ing encrinites, Spirifer, &c 210 o 



.Grey marl 15° 



1636 10 



These beds rest on the Carboniferous Limestone. 

 They were found but slightly developed to the east, 

 while at Tenby they were but a few feet thick, con- 

 sisting of carbonaceous shales and dark limestone, 

 and containing Goniatites, as if (De la Beche remarked) 

 they were a continuation of the Black-limestone 

 group of Devonshire. It may be mentioned also that 



