; 
; 

TRANSACTIONS OF THE SECTIONS. 47 
Notices of the Geology of Ireland. By Ricuarp Grirritu, F.G.S. 
Mr. Griffith directed attention to the map of the geology of Ireland, on which he 
had been so many years engaged, and to the improvements which he had been 
enabled to make on it since 1838, acknowledging with thanks the services rendered 
to him by Col. Fordyce, and Messrs. Bryce and M‘Adam. On looking at the map, 
it will be found, he said, that the conformation of Ireland is peculiar, the coast being 
mountainous and the interior flat, Taking the line from Dublin to Galway, which 
is 120 miles, the summit level is seen to be only 160 feet above the level of the sea; 
hence it is that our canals and railways have been made at an expense so com- 
paratively trifling. Lough Allan, which may be considered the source of the Shan- 
non, is 160 feet above the level of the sea; while between Killaloe and the tide water 
at Limerick, a distance of about 12 miles, the fall is only 110 feet. The average fall 
is less than six inches to the mile, a circumstance to which we are to attribute so 
many sluggish rivers, and the existence of large tracts of country flooded during six 
or nine months in the year. ‘The mountain ranges which indicate the strata of Ire- 
land run in the north from north-west to south-east, and in the county of Cork from 
nearly east to west. 
Beginning with the foundation and going to the top, it may be said that the mica 
slate, which forms the basis of all the sedimentary rocks of Ireland, occurs in abun- 
dance in the counties of Londonderry and Donegal, where it is found twisted and 
contorted in every direction by the protrusion of the granite. Mr. Griffith next 
alluded to the stratifications in the counties of Mayo and Galway, which, he remarked, 
were chiefly composed of mica-slate, granite rock, and limestone. Granite also 
occurs to the north of Galway Bay, where it is succeeded by metamorphic rocks and 
mica-slate. To the north of the grand boundary several granite rocks occur, pro- 
truding through the mica-slate and limestones. In this district there appears the 
green marble, which is only limestone metamorphosed by the action of the granite. 
Passing northward, the mica-slate is found covered by Silurian rocks. These 
rocks contain numerous fossils belonging to the Silurian system, and are succeeded 
by enormous masses of conglomerate, containing large pebbles of grey granite, some 
of them nearly a ton in weight, and perfectly rounded. The granite thus observed 
is quite distinct in its character from the granite of the district, and clearly enough 
belongs to an older period. The thickness of the Silurian strata, including the con- 
glomerate, may be set down at about 5000 feet. The speaker next alluded to the 
slates and Silurian ranges of the promontory at Dingle, in the county of Kerry, and 
described similar formations in the counties of Waterford, Wexford, and Wicklow. 
To the north of Dublin there is another slate district, similar in character to that of 
Wicklow and Wexford, and probably belonging to a lower Silurian series, though, as 
no fossils haye been discovered in it except at the south portion, its exact age remains 
undetermined. This is accompanied with the granite at the Mourne Mountains, 
which Mr. Griffith conceives to be newer than the slate. One of the most interesting 
Silurian districts in Ireland occurs near Pomeroy, in the county of Tyrone. 
Mr. Griffith next described the Old Red Sandstone, particularly alluding to the large 
district which occurs in the county of Tyrone, and which, apparently, has some rela- 
tion to the Silurian district at Pomeroy; and then pointed out on the map several 
mountain ranges which are capped by the deposit, particularly the Galtees and 
Knockmeledown mountains, Slievenish, in the west of Kerry, and districts north of 
the county of Cork. Mr. Griffith remarked that the old red sandstone is succeeded 
by the great mountain limestone district of Ireland, which occupies two-thirds of the 
entire country. The carboniferous limestone series, he observed, is altogether about 
6000 feet thick, 3000 feet of which belongs to the lower portion of the series, and 3000 
to the upper. 
He next described the several coal districts of Ireland, commencing with Ballycastle, 
at Fair Head, on the north coast of the county of Antrim. This district, which is of 
greater antiquity than any other in Ireland, had, he remarked, been worked to a consi- 
derable extent. The coal was worked by tunnels, and the beds, which were affected at 
different elevations by the protrusion of dykes of greenstone, have been nearly worked 
out, though at Murlough Bay, which contains bituminous coal, or stone coal, there 
are some beds, whether exhausted or not he had not information to enable him to say. 
The next coal district is that situated near Coalisland, in the county of Tyrone, It 
