72 Professor Epwarp Hutr—On the Nature and Origin of Beds of Chert. 
lakelets of every form and size stud the country in all directions, or form 
chains connected with each other by channels of sluggish rivers. In the upland 
districts of Sligo and Fermanagh these are replaced and represented by deep 
rock-bound hollows and swallow-holes, often connected with each other by under- 
ground watercourses opening out on the face of an escarpment, or giving birth. 
to perennial fountains, which burst forth at the base of the cliffs and flow into the 
rivers and lakes of the plains. Some of them are equal in interest and extent 
to any which are found amongst the Derbyshire, Yorkshire, or Cheddar hills of the 
same formation, but the mass of water which flows beneath the surface from Lough 
Mask into the head of Lough Corrib, and bursts forth at Cong in several fountains 
of great size, is probably not equalled by any similar under-ground river in the 
British Isles. 
In this connexion it may also be observed that not only the larger number of the 
lakes, but also of the bays and indentations of the coast-line, are formed where the 
Carboniferous Limestone prevails. Amongst these latter may be pointed out the 
Bays of Donegal, Sligo, Killala, Clew, Galway, Shannon Harbour, Tralee, Dingle, 
Kenmare, Cork Harbour, Dungarvan Harbour, Wexford, Dublin, and Dundalk. All 
these depressions along the coast occur where the Carboniferous Limestone either 
now exists, or did so originally before its place was occupied by the waters of the sea. 
As regards the lakes—nearly all those of special extent, such as Lough Erne, 
Lough Melvin, Lough Gill, Lough Conn, Lough Corrib, Lough Mask, Lough Ree, 
the Westmeath lakes, Lough Derg, and the Lakes of Killarney, rest upon floors 
of Carboniferous Limestone. Amongst these, the largest of the lakes of Ireland is 
not included; the age and mode of formation of Lough Neagh, being entirely excep- 
tional.* However great the number of lakes at present in Ireland, it must have 
been at one time considerably greater, as it is well-known from the frequent 
occurrence of beds of shell-marl below the peat bogs, that the tracts occupied by 
the bogs themselves must have originally been sheets of water, and this at a time 
when the noble Megaceros was “ the Monarch of the Glen.” 
On observing the close connexion which apparently exists between the distri- 
bution of the lakes in certain districts and the range of the Carboniferous Limestone 
it is impossible to doubt that the nature and composition of the rock is a main 
cause of the origin of such lakes themselves. Many of these lakes are true rock 
basins, such as Lough Erne, Lough Gill, Lough Mask, and Lough Corrib. Yet it 
is scarcely necessary in their cases to have recourse to the theory of glacial erosion 
in order to account for their formation. Without denying to this agency a certain 
effect in such cases, there can scarcely be a doubt that the most effectual agent in the 
formation of the Irish lakes has been water charged with carbonic acid, the solvent 
power of which has been aided by the flatness of the country and the sluggish 
character of the waters when flowing off in various directions towards the ocean. 
* For a theory regarding the origin of Lough Neagh, see paper by E. T. Hardman, r.c.s. Journ. 
Roy. Geol. Soc. Ireland, vol. iy., part 3 (new series), p. 170. 
