DEVONIAN EOCKS IN IRELAND. 
281 
Du Noyer of the Irish Geological Survey, to show 
that the strata containing Wenlock and Ludlow 
fossils there graduate conformably upwards into a 
vast thickness of schistose and flaggy purple and 
greenish sandstones, surmounted by conglomerates. 
These, from the position they occupy, must re- 
present in time the slaty and calcareous Devonian 
rocks and their equivalent the Old Eed Sandstone. 
The greenish and purple flagstones immediately sur- 
mounting the Ludlow rocks, as I assured myself by 
personal inspection in company with Sir E. Griffith, 
Mr. Jukes, and Mr. Du Noyer, are followed by a 
great thickness of those hard, green, quartzose, 
coarse, gritty rocks, with interlaminated slaty layers, 
to which the name of ' Glengariff Grits ' was at one 
time assigned. Prom their hard and semicrystalline 
character, whether they be examined in the Dingle 
Peninsula, at Glengariff, or in the lofty mountains 
(including Macgilly cuddy's Eeeks) around the Lakes 
of Killarney, it is little likely that fossils will be de- 
tected in them. They often, indeed, assume that 
aspect which by old geologists would have been 
designated ' grauwacke ' *. 
These purple and greenish grits, together with sand- 
stones and conglomerates of considerable thickness 
(the latter containing rolled fossils of the Upper Si- 
lurian rocks), constitute one physical mass. Their 
lowest part, being welded on to the Upper Silurian 
by the thin fissile strata above noted, may pass for 
the tilestones of the Silurian region of England and 
Wales. The great superior masses can only represent 
the chief Lower Devonian masses of North Devon 
and the Quantock Hills, as well as those varieties 
of the Scottish Old Eed Sandstone of Scotland, par- 
ticularly in Forfarshire, which are grey in colour, con- 
glomeratic, and slaty. In fact, these great masses, 
regularly superposed as they are to the Upper Silu- 
rian, stand precisely in the same place as the lowest 
Old Eed Sandstones near Ludlow, the oldest sand- 
stones and grits of North Devon, the grits and 
slates of Coblentz and the gorges of the Ehine, 
and the conglomerates and sandstones of Porfar- 
* All these rocks are now named ' Old Eed Sandstone ' by the Irish Geological Survey, both in Maps, 
and Sections.— January 1867. 
