50 Froceedings of the Royal Irish Academy. 



IV. — Oif Glaciation by Sea Ice. Bv Edward L. Moss, M. D. R N 

 late Surgeon H.M"S. '' Alert." 



[Read, January 22, 1877.] 



The existence of a glacier implies the co-existence of so many related 

 phenomena, that the integrity of the eridence adduced in proof of it 

 becomes of proportionate importance. 



Rounding and furrowing of rock surfaces are amongst the most 

 familiar and characteiistic records left by the flow of a glacier, and 

 much attention has naturally been directed to the possibility of simi- 

 lar markings being produced by other causes. 



Apart from the planing and striating resulting from agencies 

 unconnected with ice action, and narrowing the subject to the effects 

 of ice alone, it has been very generally admitted that either icebergs, 

 sea ice, or river ice are, under favourable circumstances, capable of 

 rounding off rocks into the " roches moutonnes." On the other hand, 

 much has been written both to prove and to disprove the production 

 of glacial scratehings by such agencies. 



So long ago as 1847, Forchhammer, writing of the scratched and 

 polished rock surfaces in Denmark, pointed oat that sea ice occasion- 

 ally forced on shore by strong gales carried boulders and dehris with 

 it, and could hardly fail to striate the rocks over which it passed. 

 Since that time Sir Charles Lyell has referred certain markings found 

 by him in the Bay of Fundy to such action, and Dr. Robert Brown, 

 and Mr. Campbell have dwelt on the probability of its occurrence. 



The shore of the Polar Sea in north latitude 82-27, where H. M. S. 

 Alert passed the winter of 1875-76, is everywhere lined with a barrier 

 reef of ice masses broken off from the floes and grounded along the 

 beach in from five to fifteen or more fathoms of water. The ice thus 

 grounded slowly wastes summer after summer from cubical into con- 

 ical and "mushroom" shapes, and as it wastes it gets forced fui'ther 

 and further towards the ice foot by the incalculably great pressui-e 

 of the Polar pack. It occasionally happens that such masses, during 

 the rough handling they are subjected to every year in the brief dis- 

 ruption of summer, or during the five months in which the floating- 

 floes retain some motion, get overturned and thus expose the under 

 surfaces which had lain in contact "with the bottom. 



Specimens of two such surfaces existed in the immediate neigh- 

 bourhood of H. M. S. Alert as she lay frozen in her winter quarters. 

 One of them formed the side of an ice cave under a large floeber«- 

 half a mile astern of the ship. The ice of the sm-face which had 

 rested against the bottom was easily distinguished from the clear blue 

 ice round it by the dark colour caused by the mud and fine sand 

 it contained, and every part of it was chiselled into deep and well- 

 marked parallel grooves and ridges, such as, had they existed in rock 



