Vol. 58.] A SUBMERGED AND GLACIATED ROCK-VALLFY. 39 
3. Nore on a Supmercen and Gtactatep Rock-Vatiny recently 
exposed to view in CARMARTHENSHIRE. By Tuomas Coprineron, 
Esq., M.Inst.C.E., F.G.S. (Read November 6th, 1901.) 
In a paper published in the Quarterly Journal for 1898°* I gave 
particulars of submerged rock-valleys in South Wales. Further 
instances of the same sort have since come to light, one of which is 
sufficiently remarkable to deserve description. It was discovered 
in building a bridge across the River Towy, at Drysllwyn, 9 miles 
above Carmarthen (to which place the tide now flows), and about 
18 miles from the mouth of the river. The sources of the Towy are 
some 40 miles from Drysllwyn, on the borders of Cardiganshire and 
Radnorshire, at about 1700 feet above the sea; but tributary streams 
descend from the Black Mountain, 2000 to 2600 feet above sea-level, 
on the south of the Towy Valley, 12 to 16 miles above Drysllwyn. 
At the bridge, the valley is narrowed by a detached hill of Lower 
Section in the Towy Valley at Drysllwyn. 
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Silurian rock rising about 180 feet above the river, which stands out 
into the valley and contracts the width to half a mile. The river 
now flows at the foot of the hill, which rises at an angle of 40° 
with the horizon, and is crowned by the ruins of Drysllwyn Castle. 
Near the water’s edge on the north of the river, the rock was laid 
pare, for the foundation of the abutment of the bridge, over an 
area of 30 by 20 feet. It sloped down gradually to 23 feet below 
summer water-level at the western or down-stream side, and it was 
glaciated in large furrows, a foot and more across, running in the 
direction of the river. The surface of the rock was smoothed and 
striated, and striated blocks of grit rested upon it. In the Boulder- 
Clay above, striated stones and scratched pebbles of black Carboni- 
ferous Limestone, like that of the Black Mountain already 
mentioned, were found. 
About 60 feet farther out in the river, borings showed that beneath 
10 or 11 feet of gravel a silty clay extended to a considerable depth, 
1 Vol. liv, pe 251. 
DZ 
