386 Proceedings of the British Association. 



Denham suggested the utility of establishing a half-tide level at 

 each port, to point out the soundings of banks, at the half tide 

 along the continuous shore. He next alluded to the error which 

 had been nearly committed, in cutting a canal from Bridgewa- 

 ter to the sea, when there were tides from a fifty feet level to 

 eighteen feet. He observed, that if the distance from the earth's 

 centre to the half-tide level was calculated, it would form a cor- 

 rect base for ascertaining the heights of the land. It would 

 form a matter for consideration, if the influence of the sun and 

 moon on the tides were withdrawn, whether or not the water 

 would recede to the half-tide level. Mr Murchison said, this 

 showed the intimate connexion between geology and geography ; 

 and that if this subject was followed up, the encroachments of the 

 sea in one place, and the increase of land in another, and the 

 rate of that increase and decrease, might yet be defined. 



Mr Griffith gave an account of a mass of shelly gravel in the 

 county of Wexford : this deposition is very extensive, stretch- 

 ing along the coast for a distance of seventy miles, and attain- 

 ing a breadth of eighteen. The following is a section of this 

 deposit : 



5 feet of clay 

 7 feet marl clay 

 7 feet marl 

 7 feet of sand 



1 1 feet of gravel, containing abundance of marine shells. 



Thursday, 13th August. — 9- Mr Williams read a notice of 

 fossil plants collected in the coal districts situated on the opposite 

 sides of the Bristol Channel, viz. of Devonshire and Pembroke- 

 shire. These remains are in either case most abundant in the 

 shales that divide the seams of anthracite coal or culm, as it is 

 provincially termed ; and the object of the author's research was 

 to ascertain whether there was any geological affinity between 

 the two fields of non-bituminous coal. After a careful investi- 

 gation, Mr Williams arrived at the conclusion that they are of 

 different ages ; that of Devon being, in his opinion, a true 

 transition coal contained in a schist, while that of Pembroke and 

 Caermarthen belongs to the carboniferous series proper above 



