82 



jng in it several shells which are eminently characteristic of the 

 lower as well as of the upper beds of that great formation, he in- 

 fers, and I think with perfect justice, that the mountain limestone 

 of the North of Ireland must be compared with the whole and not 

 with the upper part only of that formation in the North of England ; 

 an opinion I am prepared to support, by having found last summer 

 several shells (notably the Sanguinolaria undata), which are pub- 

 lished by Captain Portlock from the north of Ireland, in the very 

 bottom beds of the limestone of Berwickshire and Northumberland. 

 Confining myself to the reseai-ches of this author in the palaeozoic 

 rocks, on which he has shown so much skill, I must also request my 

 hearers to consult this volume of the Irish Geological Survey, for 

 much information respecting the overlying strata, among which 

 some new features of the Keuper formation are sketched with the 

 author's usual fidelity. 



. From the researches of Captain Portlock I turn to those of 

 Mr. Griffith, who spent many years in preparing the Geological 

 Map of Ireland, and for which he has deservedly received much 

 praise. In a very elaborate comparative table of the fossils of the 

 mountain limestone series of Ireland, presented to the Manchester 

 Meeting of the British Association, Mr. Griffith divides that series 

 into five subformations, which in ascending order ai'e the Yellow 

 Sandstone, Carboniferous Slates, Lower Limestone, Calp, and Upper 

 Limestone. He also shows that the two lower of these subdivisions 

 must, from their fossils, many of which ascend into the overlying 

 strata, be classed with the mountain limestone series, and not with 

 the Devonian rocks ; in which case, I would observe, that they must 

 also be classed with the sandstone, limestones and shale of Berwick- 

 shire, to which allusion has already been made. I am the more in- 

 duced to believe in the accuracy of this comparison, because Count 

 Keyserling and myself have this year confirmed the observation of 

 Professor Sedgwick, made in 1828*, viz. that Posidonise, similar to 

 those in the culm limestones of North Devon, exist in the middle 

 of the mountain limestone series of Northumberland. As Mr. 

 Griffith has shown that the Irish Calp, which also occupies the middle 

 place in the limestone of Ireland, contains the same peculiar fossils, 

 the parallel may now be considered as very well established, between 

 this central mass of the mountain limestone in these distant localities. 

 Drawn up as this table has been under the directions of Mr. 

 Griffith, by a diligent young naturalist of good promise, Mr. F. 

 M'Coy, there can be no doubt that it is entitled to much con- 

 sideration, and that its publication will be very useful. In refer- 

 ence to the comparison instituted by Mr. Griffith between the 

 strata of North and South Devon and those of Ireland, I may 

 observe that it is of infinite importance to the establishment of a 

 true series of equivalents, that large adjacent tracts of country 

 should be surveyed, and their fossils compared by the same obser- 

 vers, for the want of which identical species may sometimes obtain 



* See Professor Sedgwick and Mr. Murchisoii, Geol, Trans, vol. iii. p. 693. 



