250 
THE SILURIAN VOLCANOES 
BOOK IV 
feature on the ground in the interior. They are sometimes distinctly 
columnar, and vary from less than a foot to many yards in width. They 
traverse both the agglomerates and the intrusive felsites. Most of them are 
01 feLsite, sometimes cellular ; but in some cases they are dolerites. There 
IS obviously no clue to the dates of these dykes. 
the- south coast of County 
Waterford may be vastly younger than the Lower Silurian rooks through 
which they have forced their way is suggested, if not proved, by a section 
whicli IS in some respects the most extraordinary of the whole of this 
remarkable series. The occurrence of a group of red strata was carefully 
noted by the late Mr. Du Noyer at Ballydouane Bay, when he was engaged 
in carrying on the Geological Survey of that part of the country. At first 
he regarded them as belonging to the Old Bed Sand.stone, which comes on 
m great foree only a few miles to the west; but he subsequently arrived at 
the belief that they are really an integiul part of the Lower Silurian rocks 
of the district. ^ Professor Jukes had previously expressed himself in favour 
ot tins latter idea, which was thought to receive support from the occur- 
rence of .some reddish strata in the Lower Silurian rocks of Tagoat, Countv 
Wexford.^ 
The occurrence of red rocks among Silurian strata, which are not 
usually red, might quite reasonably be looked for in the neighliourhood of 
Old Led Sandstone, Permian or Triassic deposits. If these deposits once 
spread over the Silurian formations, a more or less decided “ raddliim ” of 
nm <^‘'^ken place. But in the present instance, though the 
Old Led Sandstone begins not many miles to the west, no such explanation 
of the colour of the strata is possible. The cliffs of Ballydouane Bay 
consist of red sandstone, red sandy shale and conglomerate. The red tint 
IS of that dull chocolate tone so characteristic of the Lower Old Bed Sand- 
stone. The conglomerates are immense accumulations of ancient shinole 
consisting largely of pieces of white vein-quartz and quartzite, sometimes a 
loot long and often weU water-worn. Some of the sandy beds are full of 
large scales of white mica, as if derived from some granitic or schistose 
region at no great distance. Taken as a whole, the strata are much less 
indurated and broken than the Silurian grits and shales of the district • 
some of them, indeed, weather into mere incoherent sand that crumbles 
under the fingers. There does not appear to be any positive proof that the 
red rocks are truly bedded with the ordinary Silurian strata, the junctions 
being faulted or obscured by intrusive igneous masses. 
Nowhere in the British Islands, so far as I am aware, is there a similar 
group of strata among the Lower Silurian rocks. If they beloncr to so 
ancient a series, they show that in the south of Ireland, duriim'’ Lower 
K 1 urian time, there arose a set of peculiar physical conditions precisely like 
those that determined the accumulation of the Old Bed Sandstone in the 
same region at a later geological period. And in that case it is hardly 
10 1®'’ 168, 178 and 179 of the Geological Survey of Ireland (1865), pp. 
