478 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 20", 



I may observe, that the section north and south of the bay is an 

 unequal one, so far as the Upper Old Red is concerned, though mar- 

 vellously exact in the overlying beds. On the northern horn of the 

 bay the stacks and cliffs show a great many bands of conglomerate ; 

 on the south side scarcely any, the distance being barely a mile. 

 Northward, the Old Red Sandstone is red sandstone and marl nearly 

 to the top, intermixed only with a few subcalcareous bands and grey 

 sandstone ; but on the south side each of these intercalations becomes 

 magnified, so to speak. The limestones are thicker and more fre- 

 quent, and are crowded with fossils ; the grey shales thicken out to 

 the exclusion of the red marls ; grey sandstone is abundant ; and the 

 result is that, out of 120 feet, there is not above 25 feet of red shale 

 in the upper portion of the Old Red Sandstone at this point. Then 

 follow red, green, and grey beds, in the usual fashion, all the way 

 to Freshwater *. 



By this remarkable change in the mineral character we are pre- 

 pared for a considerable change in the conditions of life. The soli- 

 tary Serpula in the cliffs of Caldy had already indicated the neigh- 

 bourhood of marine life. I found scattered specimens of the same 

 Serpula here, about 70 feet below the top ; but with it were a 

 number of other forms, familiar to me only in North Devon, namely, 

 Avicula JDamnoniensis, in abundance ; Cucullcea trapezium*! ; Khyn- 

 chonella laticosta ; Bellerophon, three species, one identical with the 

 B. bisulcatus of North Devon ; with numerous undescribed forms of 

 Pleurotomaria, Nucula, Sanguinolites, Modiola, Axinus, and Discina. 

 In beds of shale associated with these are numerous linear Plants 

 (observed first by Sir H. De la Beche), but not determinable ; they 

 extend their range into the underlying Old Redf. 



§ 3. North Devonshire. 



This change in the mineral character, accompanied by the intro- 

 duction of a marine fauna, conducts us somewhat less abruptly than 

 would otherwise be the case to the calcareous and slaty sediments on 

 the opposite coast of Devonshire. The red tint is, indeed, not wholly 

 lost in North Devon, but is confined to narrow belts of the Devonian 

 rocks. 



I crossed from Combe Martin and Ilfracombe to Barnstaple, in 

 more than one direction, and could find no red colour at all. A 

 purple tint, however, stains the belt of slate -rocks (Morte Slates of 

 Sedgwick and Murchison) which intervenes between the grey Middle 

 Devonian slates of Ilfracombe and the Upper Devonian of Barn- 

 staple and its neighbourhood. It is of these last that I must now say 

 a little, the " Marwood beds " of the above authors being the upper- 

 most strata of their Devonian system ; and these, in their grey sand- 



* It is worth while noting that the Old Red Sandstone at Freshwater, where 

 it overlies the Silurian rocks, commences with a conglomerate of Silurian peb- 

 bles. We have, indeed, plenty of evidence that there is not in Pembrokeshire a 

 continuous section from the Silurian to the Old Red Sandstone ; and in all pro- 

 bability none but the upper division of the latter formation is present. 



t Mem. Greol. Surv. vol. i. p. 107. 



