6 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 8, 



5. Blue Mud-deposit. — This is a very tenacious mass, resisting 

 the action of the sea. It is of variable thickness, increasing as it 

 passes down seawards. After most dihgent search I was unable to 

 find any evidence as to the nature of this deposit, whether fresh- 

 water or marine -, in this respect it resembles the blue-clay deposit of 

 the Bridgewater levels ; from the abundance of diffused vegetable 

 matter it has the appearance of being of freshwater origin. 



It might seem at first sight, as indeed it did to Sir H. De la Beche, 

 that the trees of the submerged forest had grown in this blue mud, 

 from the manner in which they stand out of it ; but the mud- 

 deposit surrounds the stools of the trees, which never send roots into 

 it ; and wherever the mud has been removed the trees are seen to 

 be rooted in the beds beneath. The accumulation of the mud has 

 been subsequent to the forest-growth. The uniform level at which 

 the trees have been cut ofi" may, perhaps, indicate the level of the 

 water which deposited the blue mud, and killed the trees at the 

 same time. 



6. Submerged Forest. — The interval left bare by the tide may, 

 under favourable conditions, be seen studded thickly by the stools of 

 large trees — some bare, some covered by a thick growth of sea- 

 weed, some just projecting above the mud-beds. Some are of large 

 size ; one measured 2 feet in diameter. The largest trees were 

 the oaks, which may be distinguished by the black colour of the 

 wood ; others, when split open, are red, probably alders ; from their 

 dimensions both must have grown under favourable conditions *. 



The prostrate trunks lay generally N.W., S.E., or away from the 

 opening of the valley ; they had been broken off" without tearing up 

 their roots. 



7. Angular detritus. — The flooring upon which the blue mud-de- 

 posit lies, for as far out as it can be. traced, is of coarse angular 

 rocks, instead of some form or other of water -worn materials, as 

 might have been expected ; these consisted only of fragments of the 

 splintery quartzose rocks of Dunkerry, of aU sizes, with their 

 edges and points as sharp, their surfaces as clean as if just broken ; 

 all thrown together in the greatest confusion. Part of this rugged 

 appearance may have been produced by the tides having washed 

 away some of the finer materials. All the trees are rooted in this 

 detritus ; it was the surface on which they grew, and had established 

 themselves antecedently to the changes here noticed. The nature 

 of this accumulation, if I am right in my explanation, renders the 

 Porlock Bay forest-beds of more geological interest than the more 

 extensive tracts of Bridgewater or Swansea. 



A thick coating of angular debris covers the surface of all the 

 hill -ranges of North Devon and Somerset; it is always strictly local, 

 and is simply the product of the breaking up of the surface to a 

 great depth. In places the mass of debris is in situ, — merely 

 detached ; but along some of the new roads which have been cut 

 about the sides of these ranges, sections are exposed, showing that 



* Large oat and alder characterize the Porlock valley, at present higher up 

 as along the course of the Horner stream. 



