126 DEVONIAN. 



slates," or bluish-grey and silvery slates and shales with imper- 

 sistent bands of limestone. They sometimes contain beds of grit, 

 and are here and there veined with quartz. The total thickness of 

 the beds has been estimated at 4000 feet. They rest conformably 

 upon the Hangman Grits. 



It may be remarked that in South Devon, limestone is con- 

 spicuously developed in great masses or reefs, in places passing 

 into slates ; these together form the equivalent of the Ilfracombe 

 Beds. In North Devon the limestone occupies but a subordinate 

 position. 



The fossils of the Ilfracombe Beds are many and varied. IMr. 

 R. H. Valpy has collected about fifty species.^ They include 

 Sttvmatoponi concentrica, Cyathophyllum cccspitosum, Favositcscerviconiis, 

 Hdiolitcs porosa, Cyathocrinus inacrodactylus, Tentaciditcs scalaf'is, 

 Atrypa reticularis, Rhynchondla pkurodott, R. pugmis, Spirifera 

 disjuncta, Merhia plebeia, Streptorhynchus crem'stria, S. umhracuhim, 

 Phacops Iccvis, etc. Stringocephalus Burtini gives name to the 

 Stringocephalus Limestone. 



The beds have been divided by Mr. Etheridge and named after the 

 localities in which they are best represented. Thus, resting on the 

 Hangman- Grits, we find the Combe Martin Beds (Combe Martin 

 Limestone, etc.), and succeeding these are the Watermouth Beds, 

 Widmouth Beds, Rillage Beds, Hagginton Beds (with Tentaculite 

 Beds at the base, containing Tentacidites scalaris), Helesborough 

 Beds, and Ilfracombe Beds.^ All these may be looked upon as local 

 geographical divisions of the Ilfracombe Beds. Moreover, in West 

 Challacombe Bay, north of Combe Martin, there is a series of grits 

 and shales, between the well-defined top of the Hangman Grits, 

 and the lowest limestone of the Ilfracombe Beds, which, in the 

 opinion of Mr. Champernowne, may correspond with the Lower 

 Slates of South Devon. 



The beds extend westwards to Lee Bay. Eastwards they are 

 represented in the Quantock Hills, and near Withycombe. At these 

 localities Corals have been obtained from limestone-bands by Mr. 

 J. D. Bring and Mr. S. G. Perceval.^ 



In the Quantock Hills the beds contain much grit, and at East 

 Brendon the rocks are raddled with iron-ore. 



The bands of limestone, although they form so small a pro- 

 portion of the series, are worked in many places for lime. There 

 are quarries at Ilfracombe, at Combe Martin and Challacombe, as 

 well as near Asholt, on the Quantock Hills. Near Asholt the 

 limestone is much iron-stained, and here ]Mr. Ussher has traced it 

 over a considerable area. At Combe Martin argentiferous galena 

 has been worked since the year 1294. In some places, as at 

 Kentisbury, contemporaneous igneous rocks have been noticed by 

 INIr. Etheridge ; the beds are worked for road-metal. 



1 Notes on the Geology of Ilfracombe, etc., edit. 2. See also R. Etheridge, 

 Q. T- xxiii- 605. The Rev. W. Mules, of Ilfracombe, also laboured most 

 enthusiastically among the Devonian rocks. 



2 Manual of Geology, p. 172. ^ G. Mag. 1S66, p. 184. 



