666 Professor Sedgwick and R. I. Murchison, Esq., on the 



3. A series of highly mineralized beds, with a southern dip, and extending to the granite. This 

 division is traversed by some elvans, and numerous metalliferous veins ; but there is no proof that 

 it is of an older date than the second group: indeed, judging from the sections, it only seems to 

 represent the upper part of that group reversed and mineralized by the granite, and by the causes, 

 whatever they may have been, which produced the mineral veins. 



The section from the Dodman point to the St. Austell granite, exhibits still 

 more striking phenomena, in the following order : 



1. A series of rocks dipping to the south-east, and extending from the Dodman to the cliffs 

 south of Porthmellion. 2. A series of nearly similar rocks, extending to the cliffs south of 

 Mevagissey, and exhibiting several anticlinal and synclinal lines — their most prevailing dip being, 

 however, to the north side of the strike. 3, A long ascending series, continued close to the 

 granite, in which there is a decidedly prevailing dip, and generally at a great angle, towards the 

 north. 



From the preceding facts, it appears that a line of elevation, nearly on the 

 strike of the beds, has thrown the greater part of the Killas between Veryan 

 Bay and Looe into an irregular trough ; and that the crystalline, metalliferous 

 slates skirting the south side of the St. Austell granite, instead of being among 

 the oldest, are among the very newest stratified rocks of the south-east side of 

 the county. 



Nor does the mineral structure of the country throw any difficulty in the 

 way of this conclusion. Many of the beds south-west of St. Austell are 

 coarse, arenaceous, and sometimes of a red colour. Near Pentowan there 

 is a series of coarse brown grits, almost resembling coal-measure sandstone ; 

 near Mevagissey and Porthmellion there is a coarse, dark-coloured slate, 

 with specks of mica between the layers, much penetrated by quartz veins and 

 alternating with arenaceous flagstone ; further towards Gerran's Bay are 

 thick courses of quartz rock closely resembling the masses of quartz rock in 

 the great arenaceous group of South Devon; and in Gerran's Haven we meet 

 with many very coarse arenaceous beds deeply impregnated with yellow hy- 

 drate of iron, alternating with bands of yellowish red and dark blue earthy 

 schist. The ferruginous beds are carried to the west side of the promontory, 

 where they are associated witli masses more coarse and mechanical than those 

 above described ; and the quartz rock reappears in a rugged elevation south 

 of Boswingran, and near Carhaise Bridge. We mention these facts to show 

 the mechanical nature of many portions of this deposit. Other alternating 

 portions have the usual characters of the finer chloritic slates of Cornwall. 



manganese and iron, which ranges near the following places : Polmere, west side of Tywardreath 

 Hill ; East Polmere ; Terras Hill, on the north side of Lostwithiel ; and Restormel Ground ; — the 

 course being about N.N.E. 



