TRANSACTIONS OF THE SECTIONS. 85 
__ on the opposite side; and it is remarkable that the coal on the up- 
_ throw side of the fault contains the less quantity. 
In respect to the diversity that exists in the bituminous qualities of 
the coal from different parts of the South Welsh coal basin, it is well 
known that the non-bituminous, or stone coal, is found on the north 
side and at the west end; the bituminous coal on the south side and 
east end; and there is an intermediate region occupied by an interme- 
diate quality. 
Mr. Logan has lately ascertained that, in two or more of the prin- 
cipal collieries on the south side of the basin, near Swansea and 
Llansamlet, though the lower seams of coal carry their bitumen to 
points deeper in the earth than the higher ones, they begin to part 
with it at points further to the south. And it appears to him that 
_ these facts taken together, unless contradicted by further evidence, 
_ indicate the possibility of a rule in the change of quality; namely, 
_ that it occurs in parallel planes, cutting the seams of coal without 
regard to their strike or inclination, and dipping to the south or east of 
south. 
There are two anticlinal lines, one running from Pont ar Dawe by 
Mynydd golli wartad and Llangafillach to Rhyd y mardi; the other 
from Loughor along the road towards Swansea, and then through the 
colliery of Sir John Morris at Pentre. 
In the mountain limestone, on the south side of the basin, and to 
_ the east of Cefn bryn, there are two geological waves or edges run- 
_ ning east and west. 
The millstone grit appears above the mountain limestone, along the 
_ northern line of the basin ; and it is also seen, but not so distinctly, 
_ on the southern side in Gower, and in the fractures of the rock which 
_ there represents it in Cel ifor Hill, near Llawhedian, and a few miles 
eastward wavellite is found in abundance. 
_ On the Tidal Capacity of the Mersey Estuary—the Proportion of Silt 
held in solution during the Flood and Ebb circulations—the Excess 
of Deposit upon each Reflux, and the consequent Effect produced by 
the Matter thus detected in its transit, and measured at its lodgement, 
on the banks in Liverpool Bay; with Diagrams. By Captain 
Denuam, RN. 
_ Captain Denham states the area of the Mersey, from Rock to War- 
_ rington, to be 113,171,200 square yards, and its average channel ca- 
_ pacity 535,914,040 cubic yards, that mass of water circulating to and 
_ fro four times every 24 hours. The flood occupies 5° 20'. The ve- 
_ locity on the Narrows (from Seacombe to Prince’s Terrace) is from 
1 to 62 miles per hour, amounting to a transit of 233 on flood; the 
_ ebb is for 6" 30', velocity 3 to 7 miles per hour, and the amount of 
_ transit 29} miles. The greatest velocity on the flow is at the third 
hour; on the ebb, at the second: the impetus on the flow greater after 
the third hour than before; on the ebb, greatest on the first half ebb. 
