I 



109 



from 70 to 80, but in some to upwards of 100 feet below high water) regular 

 sections were constructed by the dock engineers. In some places there were 

 two forest-surfaces divided by a bed of leafy clay from 5 to 15 feet thick. 

 We have also reason to believe that evidences of this recent easterly depres- 

 sion of a late, Post-glacial forest-surface, varied by some slight oscillations, 

 obtain further south over the area of the great fen coimtry. Unless we 

 suppose the forest at Grimsby to have grown down to the very level of 

 high water, we must allow an even greater depression than the 52 feet 

 of the Grimsby borings; and it will, we think, occur to all how material an 

 alteration, and in some parts reversal, of the earlier Hnes of Post-glacial 

 drainage such a depression must involve, if it were not equal over the area." 

 Mr. Godwin-Austen's description of the Porlock beds wliich 

 occur low down the Bristol Channel, in Somersetshire, is so clear 

 that I quote largely from it, and have constructed a section 

 from the information he has given .'^ 



I. He observes that "it has been long known that there was 

 a submerged forest beneath Porlock Bay," and, taking the strata 

 in descending order, speaks first of the shingle beach, which "is 

 composed wholly of the siliceous rocks of the coast from Porlock 

 westward, and forms a ridge round the bay." 



II. Passing to the Marine Silt, this is described as " of a 

 yellowish-brown colour, containing the shells of Scrohicularia 

 piperata, with the valves united, and of all ages. The presence 

 of these shells shews that the lower part of the Porlock Valley 

 was at one time in the condition of a mud-flat, wholly covered 

 by the sea at every tide, perhaps even permanently covered." 



III. The surface of plant growths next claims attention and 

 the following account is given : — 



" At low water and when the coast has been swept clean of shingle, there 

 is presented an expanse of mud-deposits, with the stumps of trees studded 

 about. The mud-deposits occur in patches, owing to the action of the breakers 

 which cut out portions; around these patches are good sections. The 

 uppermost mud-deposit, that with the Scrohicularice, is not very resisting, so 

 that it occurs only occasionally over the area left by the tide; enough, however, 

 remains to show that it was at one time spread out continuously with a like 

 composition and under the same conditions as are presented by the beds 

 beneath the meadows ; as such it passes down beneath the present lowest water 

 level. Under the yellow mud-deposit is a dark band, and when the mud 

 * Quarterly Journal, Geological Society, xxii., p. 3. 



