Vol. 54.] IN SOUTH WALES, DEVON, AND CORNWALL. 265- 



The Laira. 



A section was revealed by the cylinder-foundatioDS of the railway- 

 bridge, which has been described by Mr. K. H. Worth.^ The sides 

 of the rock -valley have slopes as steep as 1 in 2, and dip down to 87 

 feet below the level of low-water spring-tides, leaving a width of 

 212 feet in the middle of the river unexplored, and possibly deeper. 

 This valley is in the limestone-rock and is filled up to low-water 

 level with sand, much of it of a coarse grain. Two layers of oyster- 

 shells of considerable thickness were met with, one at about 30 feety 

 and the other at between 60 and 70 feet below the level of low water. 



Towards the Sound, the rock-bottom of Cattewater is more than 

 64 feet below the level of low water, and in Sutton Pool the rock-side 

 on the west slopes down at the rate of 1 in 2 to 60 feet below the- 

 level of low water. Complete sections are not, however, available. 



Millbay. 



Before and during the construction of the Great Western Docks 

 nine sections of the rock-bottom were made from east to west 

 about 100 feet apart, across what is now the outer basin, one along 

 the inner basin in nearly the same direction, and five across it from 

 north to south. The result was to reveal a rock-bottom in the form 

 of a valley 73 feet below the level of low-water spring-tides opposite 

 the outer pier, gradually shallowing to 46 feet at the wall of the 

 inner basin, and then bending round to the east, towards the 

 entrance of the old Union Dock, where the rock-bottom is 22 feet 

 below the level of low-water spring- tides. Inside what was formerly 

 Millbay the valley in the rock was filled up with silt to about the- 

 level of low-water spring- tides, the depth of it being from 65 feet 

 at the outer end to 27 feet near the entrance to the Union Docks. 

 In one section red clay-and-stones, about 3 feet thick, is recorded 

 under the silt. 



The lateral slopes of the valley are in places as steep as 1 in Ig, 

 and in one section 1 in 1. The inclination of the rock-bottom 

 in the longitudinal section is regular within Millbay, outside 

 which it falls more rapidly and soon joins the deep-water channel 

 which forms the entrance to Hamoaze. The greatest depth between 

 MiUbay and Drake Island is 108 feet below the level of low-water 

 spring-tides, with a rock-bottom ; but not far off, opposite Eastern 

 King Point, there is a sounding of 138 feet, and there is a deeper 

 place outside the entrance to Hamoaze. Across the entrance,, 

 between Devil's Point and Wilderness Point, the width from shore 

 to shore is only 370 yards, but the depth is 120 feet below the level 

 of low water, and the rock-bottom on the western side slopes at 

 1 in 2. The rock on each side, and presumably at the bottom of 

 the channel, is Devonian Limestone. Within the entrance, where 

 Hamoaze widens out, the shores are of Devonian shale. 



1 Trans. Plymouth Inst, and Devon & Cornw. Nat. Hist. Soc. vol. xi (1890-91)' 

 p. 66. 



