Vol. 54.] SUBMERGED BOCK- VALLEYS IN SOUTH WALES, ETC. 251 



21. On some Submerged Kock-v alleys in South Wales, Devon, and 

 Cornwall. By T. Codrington, Esq., M.Inst.C.E., F.G.S. 

 (Read February 23rd, 1898.) 



[Abridged.] 



The following particulars of some rock-valleys below the sea-level 

 were for the most part gathered by me in former years, during the 

 execution or the projection of engineering works with which I was 

 more or less connected, or well acquainted. Information has also 

 been afforded me from time to time by the courtesy of the engineers 

 of other works in which similar sections have been exposed. The 

 main object in the present paper is to put the facts observed on 

 record in a connected form. 



The details of the sections now given are, from a geological point 

 of view, more incomplete than could be wished, as must almost 

 always be the case when observations are made during the progress 

 of engineering works by those to whom they are not matters of 

 primary importance. Things observed are not always recorded, or 

 perhaps their significance is not understood until they are lost to 

 view. Notes and sections, when made, are lost sight of, cr are laid 

 aside for further information or a more convenient season, which, 

 as in the case of some of these sections, may be a long time in 

 coming. 



The localities naturally fall into two groups : — (1) on the southern 

 coast of "Wales, from Milford Haven to the Severn ; and (2) on 

 the southern coast of Devon and Cornwall, from Dartmouth to 

 Falmouth. 



I. South Wales. 

 Milford Haven. 



This estuary extends 20 miles inland, with two main branches, 

 which are fed by streams rising on the Prescelly Hills (1760 feet), 

 12 miles to the north-east. There are besides many tidal creeks, 

 locally called 'pills,' branching out of the estuary. 



The bottom of one of these, Neyland Pill, situated nearly opposite 

 Pembroke Dock, was thoroughly explored some 35 years ago by 

 borings. The rock- bottom was traced from side to side at about 

 19 places in the length of a mile from the mouth of the pill. 

 Fig. 1 (p. 252) is a characteristic example of the cross-sections.^ 



At the uppermost section of the pill, a mile from its mouth, the 

 rock-bottom is 12 feet below the level of low-water spring-tides, 

 and is covered with 23 feet of mud and silt. Each successive section 

 shows the bottom of the rock-valley deepening gradually to near the 



^ [With this paper were exhibited 45 cros^-secf on3 of valleys drawn to an 

 uniform scale, and other sectiona. Examples of these have been selected for 

 publication.] 



