GLENGARIEF GRITS AND SLATES. VI. General Conclusions. 721 From the above considerations, therefore, I am impelled to the conclusion that the great series of green and purple grits, conglo- merates, and slates which rise into the highest elevations in the south-west of Ireland are of Upper Silurian age, a conclusion pre- viously arrived at by the late Sir K. Griffith, the late Mr. John Kelly, and other geologists of eminence. Let me now briefly recapitulate the reasons *. First. These beds form but an upper member of the fossiliferous Upper Silurian series of the Dingle promontory, with which they are connected both by conformity of stratification and similarity in the composition of the beds themselves. Second. They are overlain, with the most extreme discordancy, by the Old Red Sandstone and Conglomerate, not only in the Dingle promontory, but, as I believe, throughout the south of Ireland, wherever the two formations happen to come together. Thirdly. These beds are evidently the equivalents of the Upper Silurian series (at least in part) of the region of West Galway and Mayo (" Mweelrea and Salrock beds "), including the rocks on both sides of Killary Harbour, to which they bear a close resemblance. Fourth. As these beds cannot be of Old Red Sandstone age, neither is it likely they can be the equivalents of the marine Devonian beds of Devonshire, Belgium, and the Ehine. Their place is, in all probability, below these, as I have already hinted. The most natural supposition therefore appears to be that they represent, in a greatly expanded form, the Ludlow series of the west of England and borders of Wales, and form a connecting link between the Upper Silurian and Lower Devonian formations. Fifth. The absence or scarcity of fossils cannot be regarded as evidence in any way. Fossils are very scarce amongst the upper beds of Mweelrea and Killary Harbour, except in a few localities ; but sufficient have been found to enable us to determine the age of the beds which contain them. I have also given reasons for believing that the fossils found in the conglomerate of Parkmore, near Ventry, are really of the age of the beds in which they occur. Discussion. Dr. Duncan remarked on the evidence of the occurrence of an enormous interval of time being represented by the great overlap described by the author, and stated that he did not feel disposed, on pakeontological evidence, to include the Carboniferous Slate in the Devonian.
- In a paper published in the ' Geological Magazine ' for Dccsmber 1878, 1 have
indicated the probability that the marine Devonian beds (Lynton Slates, Martinhoe beds, and Ilfracombe Limestones) fill up the gap which in Ireland intervenes between the Old Red Sandstone and the uppermost Silurian or G-lengariff Grit and Slate series. In which case the " l'ickwell-Down Sand- stone" would represent the Old Red Sandstone of the south of Ireland.
