OF THE KOCKS OP THE SOUTH OF IRELAND. 265 



that there is reason for believing that the Glengariff beds really Jiave 

 some representatives in the Devonshire section, and this in the very 

 basement beds of the whole series of strata represented in North 

 Devon, namely the Foreland grits and slates. 



YIII. The Poreland Grits, possible Eepresentatives, in part, of 

 THE Glengariff Beds. 



jN^o one who compares the Poreland with the Glengariff beds can 

 fail to admit the strong resemblance they bear to each other, except 

 for the greater predominance of grits in the former*. The section, 

 however, of the Poreland beds is imperfect ; the base is nowhere 

 visible, as shown by De la Beche ; but as far as it extends, the re- 

 semblance is almost complete. I have already described these beds, 

 and remarked on the resemblance of the plant-remains they con- 

 tain to those of the Glengariff beds. All things considered, we 

 cannot be far wrong in supposing that the Glengariff beds at the top 

 of the Silurian series of the one country are on, or about, the same 

 geological horizon as the hasement-beds of the Lower Devonian series 

 of the adjoining country. In each case they may be regarded as 

 the connecting links between the Silurian and Devonian groups, 

 and therefore as occupying a nearly similar, if not identical, strati- 

 graphical position. If this be admitted, we are now in a position 

 to complete the entire geological history for both countries, each 

 furnishing to the other the missing links in the geological chain, 

 thus enabling us to understand both the analogies and distinctions 

 in the physical events of the great period which intervened be- 

 tween the Silurian and Carboniferous epochs. 



I have endeavoured to represent in the annexed Table (p. 266) the 

 geological series of the south of Ireland and North Devon ; and to 

 avoid repetition I have placed in juxtaposition the representative 

 series in Belgium, to which I wiU refer subsequently. 



As regards South Devon, I have nothing to add to what . has 

 already been written by various authors. The North-Devon sec- 

 tion, so complete and clearly laid open, is admittedly the key to 

 that of South Devonf. As Mr. Etheridge has shown, the Middle 

 Devonian limestone of Newton Abbot and Plymouth is not only 

 more fully developed as a limestone formation than its representative 

 at Ilfracombe &c., but it contains a much larger assemblage of marine 

 fossils, while there arc grounds for believing that the representa- 

 tives of the Upper Devonian beds are less clearly represented, or 

 are concealed by faults along the margin of the Carboniferous area, 

 or, finally, are cut out by the granitic intrusions. To determine 

 these points fully will require a very careful and detailed survey +. 



* Prof. Jukes describes them as "thick massive grits of green and red 

 colours with purple slates, . . . the whole being similar to many parts of the 

 Old Ked Sandstone of the south-western portion of Iceland," meaning thereby 

 the Glengariff beds. — Additional Notes, dj'c. p. 9 (18()7). 



t Except that the " Upper Devonian Limestone" with Goniatites at Chud- 

 leigh, described by Dr. H. Holl and Prof. Eomer, seems to be unrepresented in 

 North Devon (see Geol. Mag., April 1880). 



\ Dr. Holl considers that in South Devon tliere is an unconformity between 

 the base of the Culm-measures and the underlying Devonian rocks. 



Q. J. G. S. No. 142. T 



