254 ME. T. CODEINGTON OK" STJBMERGED EOCK-V ALLEYS [Aug. iSoS^ 



At Neath a boring, made many years ago to find a foundation for 

 the railway-bridge, reached 52 feet below the bed of the river, 

 passing through blue clay and peat, and ending in gravel. More 

 recently further evidence has been afforded by trial-shafts and 

 borings along the line of a proposed tunnel under the river, and by 

 the cylinder-foundations of a bridge for the Ehondda & Swansea 

 Bay Eailway. The bridge is 1^ mile below Neath, and is 444 feet 

 long. The cylinders of the westernmost pier reached the Coal 

 Measures at 28 to 31 feet below the level of low water, and one of 

 the cylinders in the next pier, 58 feet distant, probably touched Coal 

 Measure shale ; but the cylinders of the other four piers all ended at 

 from 36 to 42 feet below the level of low water in stiff dry clay-with- 

 stones, which was found by boring in one of the cylinders to reach 

 a depth of more than 55 feet below the level of low water. The 

 bridge is on the west side of the existing valley, here more than a 

 mile wide and but little above high water. At what depth the 

 rock-bottom may be east of the bridge there is no evidence. 



The deposits passed through by the cylinders, in ascending order^ 

 are (1) the hard dry clay and stones, penetrated to about 28 feet, and 

 of unknown depth ; (2) gravel and large stones ; and (3) sandy clay 

 and mud, from about 20 feet below the level of low water upwards. 

 The large stones in (2) were of irregular shape and size up to about 

 7 feet across, waterworn but not round. The blocks in the hard 

 dry clay below (1) were similar, and the materials noticed were 

 Pennant and Grit. It is believed that the first cylinder sunk (6 feet 

 in diameter) rests entirely on a large boulder, supposed to be rock 

 in situ until other cylinders of the pier were sunk. 



I was not fortunate enough to see the sinking of the cylinders, 

 but the railway-cutting near Cwrt Sart, about a mile to the east- 

 ward, was pointed out as exhibiting the same formation. At that 

 point a long rounded hill, called Giant's Grave, rises out of the valley 

 to upwards of 100 feet. On the west of it is the river Neath, 

 flowing through marsh-land, and on the east of it is a valley some 

 20 feet higher in level separating Giant's Grave from Mynydd y 

 Gaer, rising to 1000 feet, through which the road and the railways 

 pass. The latter cut into the isolated hill, and furnish a section at 

 from 20 to 40 feet above the sea of what is (to all appearance) 

 Boulder Clay. The lower part is more clayey than the upper part, 

 but the constituents are the same: — rounded stones, gravel, and clay, 

 containing boulders and blocks of Millstone Grit, Old Red Sandstone^ 

 and Coal Measure sandstone. One boulder of Millstone Grit measured 

 2^ X 2 X 1-^ feet and another 3x2x1^ feet, and there are many, 

 some well rounded and smoothed, others subangular, up to a cubic foot 

 in size. The blocks of Coal Measure sandstone are larger and 

 more angular, though embedded in pebbles and rounded stones. 

 One polygonal block, which measured 6x5x2 feet, was covered with 

 angular and rounded stones embedded in gravel and clay. In the 

 side of the cutting there remains a block of sandstone 8 x 3 x ? 5 feet 

 plainly glaciated on the smoothed upper surface, and I also observed 

 a smaller rounded and smoothed block unmistakably striated. 



