484 



IIJ^TRTJSIYE TTJFF-LIKE EOCKS IN IRELAND. [Aug. I9OI, 



among which the tuiF-like rock was intruded in the form of a suc- 

 cession of thick sills. So distinctly is the mass as a whole not a rock 

 of purely clastic, subaerial, or submarine origin that it contains 

 masses of tuff-like rock as shown at A in the section ; and follow- 

 ing the direction of apparent dip westward along the cliff, the same 

 mass is to be observed some 50 yards off, penetrating a remnant 

 of the black slate of more important dimensions than any of the 

 included pieces, and, as is believed, occupying its natural position 

 in the stratigraphy of the sedimentary rocks. Passing the point at 

 which this exposure of black slate is seen, the succession of massive 

 layers of apparent ' tuff ' continues westward for a considerable 

 distance. 



Fig. 5. — Cliff-section at St. Eonan^s Bay, south of Tramore 

 (Conn t)/ Waterford) . 





' •" ; '.'<^.- 



'^i-''^^S'^^>i^^^ 



[Length of section = 30 yards.] 

 L=Llandeilo black slate. A= Coarse fragmental rock (' tuff '), with 



T = Fine f ragmen tal rock ('tuff') inclusions of slate, etc., and flow- 



F= Later felsite. structure at the base. 



The rocks of this coast have lately been described by Mr. F. R. 

 Cowper Reed,^ who regards some of the fragmental masses as 

 xenolithic felsites, and some as ' agglomerates.' The author refers 

 to coarse igneous breccias at Annestown as xenolithic felsites 

 (op. cit. p. 665). These were represented as volcanic ash on the 

 Geological Survey Maps, and might be taken for such. They form, 

 however, a succession of great sills such as that above described, 

 and near Carrickadurrish rock, truncate a series of calcareous slate- 

 beds, as may be well seen in the cliff, and is shown in fig. 6. This 



^ Quart. Journ. G-eol. See. vol. Ivi (1900) pp. 657-92. 



