Ill 



without tearing up their roots." The above is named "forest- 

 growths, established on detrital beds — trees of great age." 



VI. "Angular detritus. — The flooring upon which the blue mud- 

 deposit lies, for as far out as 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 all 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 estabHshed themselves antecedently to the 

 changes here noticed. The nature of this accumulation, if the 

 explanation be right, renders the Porlock Bay forest-beds of 

 more Geological interest than the more extensive tracts 

 of Bridge water or Swansea." In the above we have "the forma- 

 tion of angular detritus and its accumulation at lower levels." 



" The succession of changes here indicated corresponds with 

 that of numerous other localities in the West of England. The 

 Porlock example in addition seems to fix a relative date for a 

 part, namely, as being subsequent to the great subaerial weather- 

 ing of the surface during the Glacial Period. The elevation of 

 the land was greater at that time than at present, but by how 

 much we have no means of determining." 



" The difference of level within which the land has oscillated 

 since then need not be estimated at more than 40 feet, the 

 range between high and low water on the Bristol Channel coast 

 being taken at 33 feet. It is certain that such forest-growths 

 as pass on all sides beneath the line of low-water, could not 

 have Hved at the high-water level, but a rise of 50 feet would 

 convert the upper part of the Bristol Channel into land-surface. 

 The greatest depth at which submerged land-surface has been 

 ascertained, is about 120 feet; a rise of such amount would 

 place the whole of the Bristol Channel in the condition of dry 



