480 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [May 20 , 



than myself must be forgiven for having identified them. Sir H. 

 De la Beche was decided in his opinion of their being equivalents*. 

 This view, however, is, I think, erroneous. The Upper Pilton group 

 (No. 4) in the main represents a series unknown in Pembrokeshire 

 (compare figs. 1 & 2), or only represented by beds a few feet thick at 

 the base of the true Carboniferous slate, while its lower portion and 

 the whole of the Marwood group (No. 3) are certainly equivalent to 

 the capping of the Old Red Sandstone. I hope I shall have the full 

 concurrence of the Irish geologists in this last view ; Mr. Jukes did 

 all he could to persuade me, in South Ireland, of the intercalation 

 of group 4. I could not, however, disbelieve the North Devon sec- 

 tion, but I had misinterpreted it. 



I will now give a few of the chief fossil types, and glance at the 

 necessary conclusions. The band of pale slate at its base is an ex- 

 cellent landmark for following the broken outline of the Marwood 

 beds, from Baggy Point, where they are best exhibited, to eight or 

 ten miles east of Barnstaple. The whole country is cut up by north 

 and south faults, and by oblique faults not laid down on any of our 

 maps, but they do not confuse the sequence much. 



Either at Baggy Point, Braunton, Marwood, or Sloly quarries 

 (the last locality being best known), the Marwood beds contain the 

 following species : — 



In the calcareous sandstones (often a brown limestone), Cucullcea 

 trapezium and its varieties, C. Hardingii, Ctenodonta (Pullastrd) anti- 

 que*, Avicula Damnoniensis, Edmondia, Sanguinolites, Axinus, Mya- 

 cites, Modiola, and Orthonota of large and small undescribed species. 

 Spirifer Verneuilii and S. laminosus ? occur very rarely. The latter 

 is a Carboniferous species, as also is Rhynchonella pleurodon, which 

 is also met with in this bed, together with species of Natica, Platy- 

 schisma, Macrocheilus, Pleurotomaria, and OrtJwceras with lateral 

 siphon, chiefly, if not all, of undescribed species. Two species of 

 Belleroplion are very common, one of them being either B. bisidcatus, 

 Ecemer, or closely allied to it. 



In the greenish shales, or silty beds, are found Bornia (Calamites) 

 transitionis, Gceppert, and Lepidodendron {Knorrid) dicliotomum, 

 Haughton, and its roots. lAngula Molaf, sp. nov., is abundant, 

 and Orthonota, or Myacites, rare. Discina also occurs, and Worm- 

 burrows are exceedingly abundant. 



Above these sandstone -beds and olive shales commences the cal- 

 careous and argillaceous Pilton group. It is chiefly grey slate and 

 finely laminated calcareous sandstone ; but thin actual limestone- 

 bands, oolitic in parts, are frequent in it. Towards the bottom the 

 shale-beds are rich in Bivalves, both Lamellibranchs and Brachio- 

 pods. Of the characteristic shells Avicula Damnoniensis is the 

 most abundant species ; Strophalosia (Leptcena) caperata occurs of 

 large size, and is associated with Spirifer disjunctus, Sow., S. Ba- 

 rumensis, Sow., Productus prcdongus, Sow. (P. Christiani), Orthis in- 



* Mem. Geol. Surv. pp. 133, 140, &c. 



t Named after the Rev. F. Mules, of Muddiford, Barnstaple. Specimens are 

 in the Museum of Practical Geology. 



