ALLUVIAL DEPOSITS. 525 



The occurrence of shell-marl containing Limiicva, etc., has been observed in a 

 bog near Montgomery. ^ A Diatomaceous deposit was discovered in 1879 by 

 Mr. W. F. Lowe in Llyn Arenig Bach, a lake about midway between Bala and 

 Ffestiniog. The bed, which was exposed during the partial draining of the lake, 

 is about I foot thick, and is overlaid by a black peaty deposit. - 



Submerged Forests have been noticed at Llandrillo Bay,'^ Cardigan IBay, St. 

 Brides Bay, and Swansea Bay. Sections of peat alternating with estuarine Scrobi- 

 czdarm-clay were recorded at the Swansea docks by Mr. M. Moggridge.'* Turf- 

 pits have been worked at Newcastle in Enilyn, Caermarthen, and peat-beds occur 

 in many other parts of Wales. 



Professor Buckman discovered in the bed of the Chelt, near Cheltenham, peat 

 in which trees occurred with their roots still standing. The formation of the 

 peat was probably caused by the trees falling across the stream and damming up 

 the water, which then became a peat-bog. 



Large tracts of Alluvium extend along the borders of the Bristol Channel 

 between Chepstow, Newport, and Cardiff ; between Berkeley and Portishead ; 

 and again near Clevedon, Weston-super-Mare, Burnham, Glastonbury, Bridge- 

 water, Langport, and Ilchester, forming tracts that suggest the former presence of 

 the sea in tidal creeks or estuaries.^ 



A Submerged Forest has been noticed at Holly Hazle, near Sharpness.'' 

 Further south the Somersetshire Levels exhibit a very variable series of beds. 

 The following section at Huntworth near Bridgewater was noted in 1826 by 

 W. Baker :— 



Feet. 



Silt 16 



Peat of irregular thickness, with Freshwater and Marine Shells, 



Bones, antlers of Deer, and Wood (Alder, etc.) i 



Soft silt 9 



Gravel, containing Shells, Pottery, and bones of Horse, Ox, and Deer i 



Blue Clay, penetrated by roots and rootlets of plants 2 



Red Marl, 29 feet below the surface, which was a little below the 



level of the highest spring-tides. 



At Shapwick the Alluvium, consisting of alternations of peat, clay, sand, and 

 gravel, was proved to be 61 feet in thickness.' 



After a long continuance of heavy rains, the river Parret and its tributary 

 streams rise above their banks and flood large tracts of country ; Lann-port then 

 lies on the edge of a vast sheet of water, and Aller, close by, is an island. 

 Glastonbury Tor is not quite isolated by Alluvium, although its appearance well 

 merits the old name of the Isle of Avalon. 



In brickyards at Bridgewater the celebrated Bath bricks are made, and these 

 take their name (as I am informed by Mr. Ussher) from a Mr. Bath, the original 

 manufacturer. These bricks, which are merely shaped in the form of an ordinary 

 brick for the sake of convenience, and are used for scouring, polishing, knife- 

 cleaning, etc., are made from a peculiar kind of sandy mud obtained from the bed 

 of the river Parret, or from reservoirs into which the river overflows and leaves 

 a deposit. This consists of siliceous sand, containing occasional remains of 

 Diatomacese.® 



Peat is very largely dug in the moorlands of Somersetshire, near Edington and 

 Shapwick, between Glastonbury and Highbridge. Some of these beds have been 



' Murchison, Proc. G. S. ii. 332. 



^ Science Gossip, Oct. 1880, p. 219. 



3 Miss Eyton, G. Mag. 1868, p, 352. 



* Q. J. xii. 169. 



* R. Chambers, Ancient Sea-Margins, p. 8. 



^ W. C. Lucy, Proc. Cotteswold Club, vi. 105. 



' W. Bidgood, Proc. Somerset Arch. Soc. xxvi. (pt. 2.) 126. 



® Geol. E. Somerset (Geol. Surv.), p. 160. 



