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. 



