Vol. 51.] RAB-IOLARIAN BOCKS IN THE LOWER CULM MEASURES. 619 



The third exposure in the Dulverton district is at Blackpool 

 Copse, on the eastern bank of the River Exe, closely adjoining the 

 Exebridge Works, and about \ mile due east of the Hulverton 

 Hill Quarry. The beds in this Blackpool Quarry are of the same 

 hard, dark, siliceous rock as at Kent's Hill : they have been much 

 disturbed, and dip S. 20° W. at a high angle. Some of the chert is 

 of the striped or Leyburn variety. Very few radiolaria could be 

 seen in this rock with a lens, but thin sections show that these are 

 present in great numbers, and usually sponge-spicules also. 



(c) Ashbrittle, West Somerset. 



A short distance E.S.E. of the outcrop on the banks of the Exe, 

 at Westbrook Farm near Bampton, and at Morebath there are, 

 according to Mr. Ussher, 1 outcrops of shales (or phthanites) similar 

 to the Codden Hill Beds, but these we have not examined. Farther 

 eastwards the radiolarian rocks are shown in a quarry on the 

 summit of a hill | mile west of the village of Ashbrittle, on 

 the road to Tiverton. The beds here are very much crumpled 

 and distorted ; they are mostly of hard, black siliceous rock, with 

 some thin, soft, shaly beds intervening. In thin sections of the 

 black rock radiolaria are shown in great numbers, and they are 

 present also in some of the soft shaly beds. Champernowne and 

 Ussher mention that the village of Ashbrittle is situated on dark 

 bluish slates or thick shaly beds of the Codden Hill type, and ex- 

 hibiting its characteristic features in adjacent hill-summits to the 

 west of the village. 2 



{d) Holcombe Rogus, Canonsleigh, and Westleigh, 

 N.E. Devon. 



A short distance east of Ashbrittle the Culm Measures disappear 

 beneath the New Red rocks ; south of it, and thus farther within 

 the boundary of the Culm, are the prominent detached ridges of 

 fossiliferous greyish-blue limestone at Holcombe Rogus, Canonsleigh, 

 and Westleigh. Both Sedgwick & Murchison, 3 and De la Beche 4 as 

 well, point out the differences which these limestones exhibit in the 

 absence of carbonaceous matter and in other features, as compared 

 with the black limestones of Bampton and of the Barnstaple district 

 more to the west, and in general appearance they more nearly 

 resemble the usual types of Carboniferous Limestone, though the 

 occurrence of Posidonomya and Goniatites, discovered in these rocks 

 by the late Rev. W. Downes, 5 renders it probable that they are, in 

 part at least, on the same horizon as the Bampton, Swimbridge, and 

 Venn black limestones and shales. At the Canonsleigh Quarries, 

 not far from Burlescombe Station, there are cherty masses in the 



1 Proc. Som. Arcbfeol. & Nat. Hist. Soc. vol. xxxviii. (1892) p. 122. 



2 Quart. Journ. Geol. Soc. vol. xxxv. (1879) p. 542. 



3 Trans. Geol. Soc. ser. 2, vol. v. (1837) p. 675. 



4 ' Report Geol. Cornwall, etc.,' 1839, p. 105. 



5 Trans. Devon. Assoc, vol. x. (1878) pp. 330, 335. 



