South-western Coal District of England'. 311 



tend far from the mouths of the rivers. Thus in ascending the BruC;, its thick- 

 ness above the peat is seen to diminish, until at length it wholly disappears, 

 and then the peat alone forms the surface to a great distance. On the banks 

 of the river at Bridgewater the peat is covered by 8 or 10 feet of silt ; and at 

 Crandon-bridge drain, 2^ miles to the north-east of Bridgewater, by 14 feet 

 of a similar deposit. The stratum of peat is in these instances thin, and ap- 

 parently compressed. Monsieur de Luc mentions in his geological travels, 

 that in deepening the channel of the river Brue in order to drain Burtle-moor, 

 the workmen, after having dug to the depth of 7 feet in the sediments of the 

 river, found on the surface of the peat which lay beneath, a heap of fragments 

 of Roman pottery, with pieces of the small bricks that are used to separate 

 the vessels in the kiln. Moulds of Roman coins were found on the peat in 

 other spots. Hence it is evident that at the time of the Roman occupation 

 the surface of the peat was exposed, and protected from inundation either by 

 its own natural level or by artificial embankments ; but that since that period 

 it has been covered by new sediments to the depth of 7 feet. Mr. Anstice 

 mentioned a similar instance in which fragments of two Roman potteries were 

 discovered at the depth of 12 feet below the silt, 300 yards below Basin 

 bridge. A Roman road crossed the marshes near this point. It is itself con- 

 structed on the silt, and is now 6 feet below the level of high-water. These 

 1 circumstances do not lead to any certain conclusions, as to the former levels 

 lof the marshes and the sea, which may have been the same during the Ro- 

 linan occupation as they are at present. The marshes may then have been 

 [secured, as they now are, by sea-walls, works of which kind we have histo- 

 rical authority for ascribing to Roman power and ingenuity in many other 

 [instances. 



Of the various other more recent changes to which the earth's surface is 

 lliable, we have only to notice, as occurring within our district, the deposition 

 [of tufa from springs charged with calcareous matter. Of this a good example 

 is presented in the Nettlebridge valley, at the north-eastern foot of the Men- 

 dip Hills, opposite to Coleford, where, immediately beneath a precipitous 

 bank of mountain limestone, some rugged rocks start through the turf, which 

 prove on examination to consist of an indurated tufaceous marl, containing 

 land shells, and impressions of blades of grass and other vegetables. 





VOL. VI. 2s 



