Correspondence. 235 



principal ones, are omitted ; as also are the traces of the strictly 

 local glaciation among the mountains. The dotted arrows indicate 

 the direction of the drift transportation; in most cases, certainly, 

 and in the rest most probably, it is the movement of the Boulder- 

 clay which is given. Since the three kinds of phenomena always 

 agree so remarkably as to direction, they must be effects of a common 

 cause ; and, therefore, they may be used jointly or separately, as 

 opportunity occurs, in tracking the courses of the streams by which 

 they have been produced. 



Those streams must have consisted of glacier ice ; because various 

 considerations shew that no other agent is capable of doing everything 

 that has been done, and of moving as the streams have moved. The 

 univei?(sal glacier was, probably, not less than 3,000 feet in depth. 

 It was, at its greatest development, but little dependent on the 

 mountains, as sources of supply ; it was sometimes inconvenienced by 

 them as obstructions to its movement. Its tendency was to spread 

 outwards in every direction, without much regard to the general slopes 

 of the open ground. As a result of its great depth and magnitude, 

 its mobility must have been vastly greater than might be sup- 

 posed possible on first thoughts, and sufficient to enable its different 

 flows to move as shewn on the map. Those flows formed a con- 

 nected, though not single, system — their mutual interference has 

 sometimes affected their movements quite as much as the resistance of 

 the masses of elevated ground. Thus, the stream which flowed south- 

 ward, near Carrick-on-Shannon (c), has divided, without having 

 be'en compelled to do so by anything in the shape of ground there- 

 abouts. The right branch of that stream has turned sharply away 

 from the wide plain before it, and flowed directly towards, and then 

 across, the (not very elevated) range of the Ox mountains, Sligo 

 (xx). The stream, which flowed eastward from near Loughrea (l), 

 has behaved in a somewhat similar manner. There were, however, 

 radiating district ice-systems, belonging to some of the mountain 

 groups ; of which the most remarkable was that of Kerry and W. 

 Cork. These may have existed dm-ing the height of the glacial 

 development, or they may not have been established until afterwards. 

 They were older than the submergence in the glacial sea ; and older 

 still than the local corry glaciers, of which we have evidence in so 

 many places. To explain fully the movements of the flows of the 

 general ice-envelope, it seems necessary to suppose that the west side 

 of Ireland was formerly higher, relatively to the east, than it now is. 

 Some independent considerations confirm this supposition. It is 

 most probable that the ground near the head of what is now Galway 

 Bay occupied a somewhat central inland position during the period 

 of the general glaciation. — Faithfully yours, M. H. Close. 



Newtown Park. Black Eock, 

 Dublin, April 9th, 1867. 



