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



series. A detailed section of the whole coast, from the head of St. 

 Austell Bay to the Dodman, might perhaps throw some new light on 

 the questions I am here discussing ■; and such a section I hope to 

 receive from my friend Mr. Whitley. Meanwhile the following notes, 

 with the accompanying outline-sketch of the succession of pheenomena 

 seen to the south of St. Austell*, are the best evidence I have to oifer. 



Near St. Austell, and thence down to Pentuan, the prevailing dip 

 is towards the north, and the highly mineralized beds do not appear 

 to hang from, but generally towards, the granite (see fig. 2). From 

 Pentuan to Mevagissey there is the same prevailing northern dip. In 

 Mevagissey Harbour the slate-rocks are nearly perpendicular, with 

 breaks and shifts of strike, indicating faults ; but on the south side of 

 the harbour the dip is steadily Magnetic North, at a great angle 

 (about 80°). This northern dip (interrupted by two undulations) 

 prevails towards Porth Mellion. On the north side of the Porth the 

 beds dip Magnetic North, at a very high angle. At the Haven Head 

 the rocks are perpendicular, and seem to belong to the pommel of 

 a broken saddle. On the south side of Porth Mellion the dip is 

 nearly Magnetic South, and at a high angle. From this part of the 

 coast there is a prevailing southern dip, and generally at a high angle, 

 as far as the extreme point of the Dodman. South of Porth Mel- 

 lion there are, however, two changes of dip, and the anticlinal and 

 synclinal lines are marked by the presence of fractures and innume- 

 rable quartz-veins. Both of these changes come in between the 

 Porth and the farthest low headland that is seen from it towards the 

 south-east. 



All along the coast, from Pentuan as far as this low headland, the 

 rocks have nothing peculiar in their structure to indicate an age dif- 

 fering from that of the best-known Devonian rocks of Cornwall ; but 

 at this headland the beds become coarse and sandy, like the beds 

 which underlie the quartzite in Gerrans Bay ; and beds of like kind, 

 striking at a high angle, and with a steady dip towards the south, are 

 carried under the quartzite of the Great Carn. And thus we are con- 

 ducted to the fossiliferous group between Peraver and Gorran Haven. 



Beyond Gorran Haven the southern dip continues ; but the lines 

 at the south end of the accompanying sketch, fig. 2, are put in from 

 memory, as I have not visited the coast south of Gorran Haven since 

 1836. 



Such are the facts (so far as I can pretend to have observed them), 

 presented by a very perplexing part of the Cornish coast. There is, 

 we believe, no trace whatsoever of any great anticlinal axis, bringing 

 up a series of older rocks among the newer Devonian slates of the 

 country ; and we cannot regard it as a reasonable hypothesis, to sup- 

 pose that such a group of fossils, as has been given above, can be- 

 long to a true Devonian System, in the sense in which these words 

 were first used by Sir R. I. Murchison and myself. 



To explain the difficulty three hypotheses suggest themselves for 

 consideration. 



* See also Tr. Geo!. Soc. N. S. vol. v. p. 666, and Geol. Rep. Cornwall, &c., 

 pi. 2. f. 3 (S. end of Section). 



