248 NATURAL SCIENCE [October 
of the objections, will perhaps be found to apply to Ireland as to 
Scotland and Sweden; it will, at all events, be found to explain 
some phenomena not easily reconcilable with other theories. Take 
the case of the large erratics frequently perched on the top or sides 
of eskers and similar deposits. When I have read that such blocks 
had been borne by ice-rafts which, stranding on the eminences, 
there melted, and dropped their burdens, I have asked without 
being able to find an answer satisfactory to myself: How could 
so slender and fragile a structure survive the rude impact of an 
iceberg? On Hummel’s hypothesis I can satisfy my own mind at 
least. I can understand how crevasses would wear and widen into 
tunnels,—how the water flow derived from the melting ice would 
sweep the morainic matter into these tunnels,—how the melting 
would vary with the season——how the solid matter would vary 
from time to time with the force of the water,—how there would 
be strata dipping towards the sides which would wear away un- 
equally at different sections,—how even on the same line of crevass 
we may find a well-formed ridge, a mound, or a heap of morainic 
matter,—and how the greater blocks would remain on the ice- 
surface, till let down on the surface or side of the ridge. I am not 
sure that we can so easily account for the roundness and smoothness 
of most of the pebbles as we could on the hypothesis of marine 
action. And I am still at a loss to know why the true esker is 
confined to the comparatively narrow midland zone.1 Surely there 
were crevasses and morainic matter elsewhere, and the great thaw 
would be general and pretty nearly equal all over the area of 
Ireland. It is easy enough to conceive that the greater part of the 
products of glaciation would finally become scattered about, levelled, 
or, in some places furrowed, by the floods which would cover all the 
low-lying parts of the country with deposits of sand, gravel, and 
shingle. Perhaps it may yet be shown that eskers were formed 
in other parts of the country, but were destroyed by local glaciers 
of later date, or by other causes. In parts of Ulster, Co. Monaghan 
for instance, there is abundance of limestone gravel in hillocks and 
mounds. That there are no long narrow ridges at present does not, 
perhaps, justify the assumption that there never have been any 
there. The preservation of an esker is, or ought to be, not less a 
subject for wonder than its original formation. 
I have already partly described the great drift formations at the 
College near Athenry, and I give some further details, which may 
afford additional illustration of Hummel’s theory. This group 
consists of two great parallel ridges running westward from the 
1 Some well-formed eskers may be seen adjoining the railway between Tuam and 
Claremorris. The locality may, however, be regarded as a portion of the great midland 
plain. 
