GLENGARIFF GRITS AND SLATES. 721 
VI. Generat Conciusions. 
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 R. 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 Rhine. 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 palzontological evidence, to include the Carboniferous Slate in 
the Devonian. 
* Tn a paper published in the ‘ Geological Magazine’ for Decomber 1878, I 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 
Glengariff Grit and Slate series. In which case the ‘“ Pickwell-Down Sand- 
stone” would represent the Old Red Sandstone of the south of Ireland. 
