Vol. 54.] IN SOUTH WALES, DEVON, AND COBNWALL. 257 



The deposits over the rock-bottom are recorded in sections made 

 when the cylinders were being sunk. At the main piers both 

 sandstone and limestone are covered with 4 or 5 feet of what is 

 called red marl, but it may be more accurately described as stiff, red, 

 sandy cJay. Over that is a layer of 3 feet of boulders and coarse 

 gravel in red clay, some of the boulders being of conglomerate, 

 others of sandstone and red limestone, one more than 6 feet across. 

 Then comes 4 feet of fine gravel (limestone), over which is a bed 

 of leaves, timber, hazel-nuts, roots, and branches. This bed is 

 22 feet below the level of low water, or more than 62 feet below 

 high water ; it is covered with coarse sand, which passes upward 

 into soft grey sand and clay, over which are silt and mud to 6 or 

 8 feet above low-water level. 



At the next pier (fig. 4, p. 258), red sand, sandy clay, and gravel 

 overlie the limestone, the surface of which is broken up. In one 

 cylinder a sandstone-boulder (6 feet across and 2 feet thick) rested 

 on the limestone embedded in this deposit, and in another a piece of 

 sound oak 8 or 9 inches in diameter lay across the cylinder close to 

 the rock, covered with 2 feet of red sand-and-gravel. In each of the 

 three cylinders of this pier, over the red sand-and-gravel, and 2 or 

 3 feet above the Hmestone-rock, there is a layer of 6 to 10 inches of 

 hard blue clay, and over that grey sand and silt with a few small 

 shells, stalks of plants (probably sedges), hazel-nuts, and wood. 

 Above low- water level the silt becomes more muddy ; it reaches 

 28 feet above that level, making the total thickness of the deposits 

 over the rock at this pier 45 feet. 



At the westernmost pier (fig. 5, p. 258) the solid limestone is over- 

 lain by a few feet of broken rock in dry sandy clay, over which is 

 coarse gravel with clay and a few boulders, and then sand and clay 

 with more boulders of sandstone and conglomerate. At 3 feet 

 below the level of low water this is succeeded by a bed of stiff, sandy, 

 blue clay, 3 to 5 feet thick, with stalks of plants (probably sedges), 

 and over that blue silt, clay, and mud reach to above high-water 

 level, making a total thickness of 55 feet over the rock. 



The boulders of conglomerate and sandstone probablj'- are derived 

 from the Old Eed Sandstone beds which are exposed higher up the 

 Wye Valley. 



The Severn. 



At the mouth of the Wye, the Severn is but shallow, with a 

 sandy bottom, but just above, near Chapel Island, there is 54 feet of 

 water at low-water spring-tides, and below, halfway between the 

 Wye and the Severn Tunnel, the chart shows a sounding of 82 feet 

 at low water. 



At the Severn Tunnel, 2| miles below the mouth of the Wye, a 

 complete section of the river-bottom was made.^ For 1| mile on 

 the eastern side the bed of the river consists of bare New Eed 

 Sandstone rock well above low water, called ' The English Stones.' 



^ See T. A Walker, ' The Severn Tunnel.' 



v2 



