GEOLOGICAL RELATIONS OF THE KOCKS OF THE SOUTH OF IRELAKD. 255 



17. On the Geological Relations of the Eocks of the South of 

 Ieeland to those of Nokth Deton and other British and Conti- 

 nental Districts. By Professor Edward Hull, M.A., LL.D., 

 P.R.S., &c., Director of the Geological Survey of Ireland. 

 (Read March 10, 1880.) 



I. Introduction. 



Baying in a former communication to this Society* endeavoured to 

 prove that the great series of purple and green grits and slates 

 which form the southern highlands of Ireland belong to the Upper- 

 most Silurian period, and that between them and the succeeding 

 beds of the Old Red Sandstone there occurs everywhere a wide 

 hiatus (a gap of unrepresented geological time), indicated not only 

 by visible unconformities but also by absence of intervening beds at 

 various points, it now becomes desirable to inquire, and, if pos- 

 sible, to determine what formations in. other districts may be sup- 

 posed to fill up the hiatas above referred to, and then, having de- 

 termined this point, to see what inferences may be drawn concern- 

 ing the physical geology of the regions referred to at the various 

 stages indicated both by the presence and the absence of consecutive 

 strata. 



This inquiry naturally leads one to cast a glance at the neigh- 

 bouring coasts of England and Wales as the districts where light 

 may be looked for on these questions ; and I propose in the follow- 

 ing pages to make a comparison of the series of beds in both coun- 

 tries, namely the South of Ireland and North Devon, and adjoining 

 dLstricts north of the Severn t. It wilV also be desirable, with a 

 \dew to a fuUcr investigation, to refer, when necessary, to the Devo- 

 nian and Carboniferous series as it occurs in Belgium and Scotland, 

 and to see how far it is comparable with, and sustains oiu: observa- 

 tions of, the Devonshire section. 



Vieivs of i^revious Authors. 



Previous Investigations. — It is almost unnecessary for me to ob- 

 serve that there are few districts of the British Isles which have 

 received more careful scrutiny, and are the subjects of more elabo- 

 rate memoirs, than those of jS'orth Devon and West Somersetshire, 

 and I am therefore happily relieved from the necessity of any at- 

 tempt at lengthened description. The geological literature of the 

 district has been carefully summarized by Mr. Etheridge in his 



* "On the Geological Age of the Rocks forming the Southern Highkmds of 

 Ireland, generally known as the Dingle Beds and Glengariif Grits and Slates," 

 Quart. Journ. Geol. Soc. vol. xxxv. p. 699 (1879). I find that Prof. Ralph Tate 

 states, with much precision, that the Dingle beds are the equivalents of the 

 " Tilestones of England, South Wales," &c. (' Historical Geology,' Weale's series, 

 p. 72). I was unaware of this when my former paper was pubUshed. 



t I confine my observations to North Devon, as it furnishes the key to the 

 structure of South Devon and adjoining parts. 



