ETHERIDGE DEVONIAN ROCKS AND FOSSILS. G61 



is known and recognized by all palaeontologists, this doubtless 

 arising from the littoral and sublittoral habits of the Invertebrata, 

 and their migration or change under diiferent bathymetrical and 

 other physical conditions as regards land and water, i^orth and 

 South Cornwall possess 2''>i species in common with the Middle and 

 Upper Devonian of North Devon. They are placed in their re- 

 spective positions in Table II. pp. 616-634, so as to complete the 

 evidence ; and it is only in the Upper Devonian beds of Petherwin, 

 Tintagel, &c. that the species approach and have passage affinities ; 

 they are generally true Upper-Devonian forms, and have been well 

 determined. It will also be seen that of the 27 species found in 

 the Ilfracombe group only 4 are common to it and the beds south 

 of Morte Bay as well as to the '■'• Carboniferous slates." These 

 are stated above, and need no further comment. 



I will embody in one Table (IX., p. 669 et seqc[.) all the known spe- 

 cies in the Lower, Middle, and Upper Devonian series of Forth Devon, 

 and include also the Upper Devonian species of Petherwin in a sepa- 

 rate column, and indicate those that pass up and occur in the passage- 

 beds between the Devonian and Carboniferous of the same area, 

 admitting that the Barnstaple beds, and all south of them to the 

 latitude of Yenn and Swinbridge &c., belong to the Carboniferous 

 group, as determined by Sir E. Murchison and Prof. Sedgwick in 

 the year 1836*. "With these Devonian species I have collated those 

 recognized as belonging to the Carboniferous Slate of Ireland and 

 the Coomhola Grits which are associated with them, in other words 

 recurrent formsf. This Table will go far to show us, if it does not 

 prove, that these so-caUed Coomhola species of Ireland are chiefly, 

 if not entirely, derived from the typical Upper-Devonian fauna — 

 from that group which so conspicuousl}' and conformably rests (in 

 North Devon at least) upon the unfossiliferous Upper Old lied Sand- 

 stone of Morte Bay. 



The assertion of Prof. Jukes, in his '' Notes for a Comparison " 

 &c.q:, that all the species occurring in the rocks above the Yention 

 Old Eed Sandstone are those of the Carboniferous Slate, with those 

 of the Coomhola Grits in the lower parts, is based upon the fact 

 that the Irish species are compared with those of North Devon, 

 and referred to them as the types. The 97 species named in his 

 " Fossils of the Carboniferous Slate," page 22 §, and referred to 8 

 localities (p. 17) in North Devon, and one locality (Petherwin) in 

 North Cornwall are, without exception, well-known and recognized 

 Devonian species, no one form occurring in the so-called Coomhola 

 Grits or Carboniferous Slate of the typical Irish area. In this list 

 there are 84 species catalogued as helomjuuf to rocks of this age ; yet 

 not one occurs either in these lower members of the Carboniferous 

 group, or in the Carboniferous Limestone of any area : it is simply 



* These beds were called " Greywiicke" by most AA-riter.s up to tlie time of 

 De la Becbe, who also retained the title in his ' Ropoi't on the Geology of Corn- 

 wall,' &c. t In the colunni headed " Carboniferous generally." 



\ " Notes for a Comparison between the Rocks of the South-west of Ireland 

 and those of North Devon and of Rhenish Prussia," &c., Journ. Roy. Geol. See. 

 Ireland, 18G5. § Ibid. 



