10 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 5, 



dip towards or under them. Farther south, and along the western 

 shore of St. Austell Bay, we find several elvan-dykes, one appearing 

 to branch off like a granite-vein, — another containing fragments of the 

 killas, through which it has broken its way to the surface. The 

 whole section, as far as the Dodman, indicates the action of more 

 than one great disturbing force. There was an elevating force pro- 

 truding the St. Austell granite ; and, if I interpret the pheenomena 

 correctly, there was a contemporaneous elevating force, acting from 

 the south ; and between these two forces, the beds, now spread over 

 the surface from the St. Austell granite to the Dodman and Nare 

 Head, were broken, contorted, and placed in their present disturbed 

 position. With these preliminary remarks I proceed to notice the 

 phaenomena presented by the rocks which descend towards these two 

 headlands. 



A few fossils have been found on the west side of St. Austell Bay ; 

 we believe them to be Devonian ; and we do not think it possible to 

 interpolate any rocks of an older epoch in this part of the section ; and 

 we apply the same remark to a large group of rocks, which range 

 through the interior of the country from the N.W. side of St. Austell 

 Bay to Veryan. Starting with this assumption, we began our exami- 

 nation of the coast between Gerrans Bay and Gorran Haven, under 

 the guidance of our friend Mr. Whitley, of Truro. Our work com- 

 menced in Gerrans Bay ; and near the road leading from the sea-shore 

 to the village of Veryan we found one of those numerous raised beaches 

 which are met with along the Cornish coast. 



The prevailing rock along the north-eastern part of the bay was 

 a bluish-grey slate (killas), much penetrated, here and there, by quartz- 

 veins, and puckered and contorted in its subordinate parts, but on the 

 whole dipping steadily to a point about 10° east of magnetic S. 

 at an angle of 40°. To the north of this group, on the road towards 

 Veryan, the beds are still more puckered, more highly inclined, and 

 contain concretionary masses, and thin bands of limestone. But 

 neither among these beds, nor at Veryan, did we find a single fossil. 

 Their prevailing strike is 15° or 20° east of true N., and the dip as 

 before is constantly to the S.E. side. 



Returning to the section along the eastern shore of the bay the 

 blue killas is followed, to all appearance, in ascending order by a 

 coarser arenaceous greywacke, sometimes very ferruginous and de- 

 composing ; and here and there it is associated with a flaky conglo- 

 merate, exactly like many of the conglomerates commonly found in 

 North Wales and Cumberland among the oldest slates. Over the 

 preceding rocks comes a remarkable, white quartzite, 30 or 40 feet 

 thick, dipping nearly S.E., and the quartzite is overlaid in its turn by 

 earthy and ferruginous slates, by conglomerates almost passing into 

 trap-shale (or schaalstein), and by very ferruginous beds of trap. Of 

 rocks like these there are several alternations, to the extreme head- 

 land, which prove that the trappean and aqueous rocks were con- 

 temporaneous ; and they preserve the same south-eastern dip to the 

 end of the section. The rocks here described, when considered 

 mineralogically, have, perhaps, an older look than the ordinary 



