360 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 3, 



Devon, and "West Somerset;" but the plan of that work was, of 

 necessity, hmited in a great degree to general views. To have entered 

 into detailed descriptions of local phsenomena, in so large a field, 

 would have required the labour for many years of several observers 

 in the investigations, and the results would have filled many volumes 

 of description. The author of that Report has however dwelt 

 upon many of the more remarkable places where the phseno- 

 mena throw light upon important questions of theory ; but, in these 

 days, when geological researches demand far more minute observation, 

 when, as our President has on more than one occasion inculcated, 

 the ground must in many cases be gone over inch by inch, ample 

 opportunities will long remain for diligent observers to fill-in details 

 in the masterly outlines of the geology of the West of England, 

 which have been drawn by the skilful and practised hands of De la 

 Beche, Sedgwick, and Murchison. A short residence in the neigh- 

 bourhood of Plymouth enabled me to examine with some care the 

 portion of the coast I am about to describe ; and believing that an 

 account of the somewhat uncommon appearances which the rocks 

 exhibit may not be without interest, and may be the means of calling 

 the attention of geologists to a more close investigation of them, I 

 venture to lay before the Society the results of my observations*. 



In Cawsand Bay, on the western side of Plymouth Sound, there 

 occurs an association of igneous and sedimentary rocks which present 

 phsenomena illustrative of some of the great questions of geological 

 theory. The portion of the coast I am about to describe extends 

 from Penlee Point on the south-west to Redding Point on the north- 

 east, a distance of about three miles, in a semicircular luie, the shore 

 being bounded by vertical cliffs, except in a few places near the fishing 

 villages of Kingsand and Cawsand. 



The prevailing rocks are red slates, sandstones, and conglomerates, 

 belonging to the Old Red Sandstone or Devonian system. These 

 sedimentary deposits are associated with a red porphyritic rock, 

 which presents itself under a variety of aspects. 



Near the eastern end of Kingsand, argillaceous schistose rocks stand 

 out on the shore, bearing W.N.W., with a S.S.W. dip. They exhibit 

 many varieties of colour, purple, red, green, and yellow ; and, in a face 

 of the rock on which the houses of Cawsand are built, all this diversity 

 of tint is well exhibited. Interstratified with shining argillaceous 

 slate are some hard arenaceous beds, uudistinguishable in colour and 

 mineral structure from many found both in the Old and the New 

 Red Sandstone formations, and, Uke them on many occasions, they 

 have stripes and spots of a greyish-white and bluish-green colour. 



Proceeding eastward, we come upon a red porphyiy, occupying a 

 considerable portion of the shore over which the tide flows. When 



* These observations were made as far back as the year 1841, and this paper, 

 so far as concerns the descriptions, was drawn up shortly afterwards, while the 

 impressions I had received were still fresh, and my notes could mth safety be 

 extended. It was laid aside for revision, but other pressing engagements inter- 

 fered, and in changes of my residence the paper and the specimens I had collected 

 were mislaid, and have only recently been recovered. 



