4 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 8, 



beneath Porlock Bay : it is indicated in the Ordnance Map of Great 

 Britain, as also in the Admiralty chart. Sir H. De la Beche gives 

 the following short account of it : — 



" At Porlock a small submarine forest is well exhibited at very 

 low tides, the stumps of trees, which appear chiefly oaks, standing 

 in the positions in which they grew. The present action of the sea 

 has bared these trees, by removing the sand and silt which once 

 covered them, as can be seen by the continuation of the same bed 

 of vegetable matter inland, beneath sand and silt, behind the pre- 

 sent shingle beach, that merely reposes on the inclined plain of the 

 submarine forest*." 



From a recent examination, the evidences of geological changes at 

 this place appeared to me to require somewhat fuller detail than is 

 given in the above ; besides which, they better serve to illustrate 

 the nature and order of -oscillations of small amount, which have 

 taken place at times shortly antecedent to the present, than do the 

 instances of Bridgewater or Swansea bays. 



The Porlock valley, viewed from any of the heights around, pre- 

 sents at its lowest level a line of coarse shingle, ridged up above 

 ordinary high water by gales and high tides. 



Within this barrier are grassy flats. Purther in, these are bounded 

 by a rise in the ground of from 10 to 15 feet ; above this the surface 

 of the ground slopes gently towards the hills, forming an under- 

 terrace to them of variable width, being broadest and thickest oppo- 

 site the openings of the deep guUies which score the rounded forms 

 of these hill-sides. 



These features are severally connected with the geological history 

 of the valley. 



Within the shingle ridge, broad water-courses have been cut across 

 the salt-pastures, and good sections of the under-terrace may be 

 seen along the water- courses, and in the low cliff from Porlock Quay 

 eastwards. Beyond the shingle, and when tides are low, and the 

 coast has been swept clean, the Porest-beds are well exhibited. 



The chronological order is as follows (in descending order) : — 



Shingle bank. 



Marine silt. 



Surface of Plant-growth. 



Fresh-water mud-deposit. 



Forest-growth. 



Angular detritus. 



2. The Shingle. — The shingle-beach requires passing notice in re- 

 spect of its position. It is composed wholly of the siliceons rocks of 

 the coast from Porlock westward, and forms a ridge round the bay. 

 On the land-side it ends abruptly, as if encroaching on the meadows ; 

 seawards it thins away, so that at extreme low water but little 

 shingle remains, and in the offing the sea-bed is composed of sand 

 and fragmentary shells. 



The shingle, where now thickest, has been heaped up upon the 

 surface of the meadows, no marine shingle of earlier date is any- 



* Report on the Geology of Cornwall, Devon, and West Somerset, p. 419. 



