THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE VI. VOL. II. 



No. IX— SEPTEMBER, 1915. 



^" 



ORIG-IWAL AETICLBS. 



N- a 



I. — Note on the Silurian Inlier near Cardiff. 



By F. J. North, B.Sc, F.G.S., Assistant Keeper, Geological Department, 

 National Museum of Wales. 



(PLATE XIII.) 



fMO the north and north-east of Cardiff there is a small inlier of 

 JL Silurian rocks (described in detail by Professor Sollas in 1879 l ) 

 covering an area of rather more than two square miles. There are 

 representatives of both the Ludlow and the Wenlock Series, and the 

 general dip of the beds is towards the north, in which direction 

 Ludlow mudstones pass with apparent conformity beneath the Old 

 Eed Sandstone. 



That there was a considerable underground extension of strata 

 older than the Old Red Sandstone was inferred from the fact that 

 grey mudstones containing fossils ("brachiopods and encrinites "), and 

 regarded as of Silurian age, had been recorded immediately beneath 

 the Trias in deep borings in the vicinity, viz. Crown Duel Works, 

 Roath Dock 2 ; Crawshay Street 3 ; and the Ely Paper Mills * ; but 

 there was no definite evidence as to the structure and extent of the 

 concealed rocks. (The sites of these borings are indicated on the 

 accompanying Map, Plate XIII, by A, R, and C respectively.) 



The dip of the Wenlock Reds in the southernmost exposures at 

 Pen-y-lan is toward the south, 5 but this does not necessarily imply 

 that a southerly dip would prevail, since minor folds have been 

 noticed further north. In the Survey Memoir 6 we read: "... it 

 by no means follows that the main axis of the Silurian inlier has 

 been passed ; \_at Pen-y-lan\ rocks older than any exposed at the 

 surface may crop out under the New Red Marls at Roath." 



Important evidence bearing upon this question has recently been 

 afforded by a deep boring for water, full details of which will be 

 published later. The boring, which was discontinued in December, 

 1914, after having reached a depth of 627 feet without encountering 

 water, was made on the site of the new premises of Messrs. S. A. 

 Drain & Co., who generously placed the cores at the disposal of the 

 National Museum of Wales. 



1 J. W. Sollas, Q.J.G.S., vol. xxxv, pp. 475-507, 1879. 



2 The Country around Cardiff (Mem. Geol. Surv.), 1912, p. 99. 



3 Ibid., p. 100. 



4 Ibid., p. 99. 



5 J. W. Sollas, Q.J.G.S., vol. xxxv, p. 477, 1879. 



6 The Country around Cardiff (Mem. Geol. Surv.), 1912, p. 5. 

 DECADE VI. — VOL. II. — NO. IX. 25 



