TBANSACTIONS OF SECTION C. 529 



would be thrust forward so long- as the glacier exerted considerable pressure by its 

 gravitation. But as it thinned out, this pressure must have gradually diminished 

 until it became nil, when the depth of water and thinning of the ice effected 

 approximate flotation. Then the mud, &c, would be deposited, and the shallowed 

 sea woidd form a submarine plain of the neutral depth over which the glacier would 

 just lightly slide and thus form a striated pavement of till. 



If the conditions remained constant, this deposit would continue level as we see 

 it at Bodo and other places in Norway ; but if climatic or other conditions fluctuated, 

 the varying advance and recession of the glacier and its varying pressure would 

 produce a ploughing up of the soft material into submarine ridges such as abound 

 in the Irish bays that are mouths of the great glaciated valleys, and are also found 

 so abundantly on and near the coast. 



The islands of Clew Bay are specified as striking examples of this. 



Having lately met with an account of a tradition which describes a great fresh- 

 water lake on the present site of Galway Bay, and having already noted many of 

 these long ridges of till in that Ray, the author revisited Galway with the object 

 of further examining them in reference to the tradition which states that the fresh- 

 water lake was converted into a bay by the sea breaking through the boundary or 

 bar that had previously separated the fresh from the salt water. 



The general result of this exploration of both shores of the Bay and several of 

 its islands was, that tbe existence of such a barrier or of a series of such barriers 

 appears very probable; but their position does not indicate so large a lake, as the 

 traditionary Lough Lurgan which is described as one of the three great lakes of 

 Ireland. 



The outermost barrier probably stretched from the cliffs of Barna (which are 

 formed by the sea washing away one of these ridges of till and exposing a fine 

 perpendicular section about 50 feet thick) to Aghinish Point, meeting the Kilcro- 

 gan promontory on the way, when this ridge of drift extended much farther west- 

 ward, as its present truncated headland of till indicates that it must have done. 



These, and other minor headlands of till, all the obvious remains of promontories 

 that have been cut off, are connected by a bar that stretches obliquely and irregu- 

 larly across the Bay from Barna, in County Galway, to Finvarra Point, in County 

 Clare. 



The promontories and island ridges do not extend fairly, across the Bay, but lie 

 in a direction from E.N.E. to W.S.W. They are still so numerous and extensive 

 as to visually overlap each other and present the appearance of an inner bar, en- 

 closing the inner bays of Galway and Kinvarra. This occurs when they are viewed 

 from the shore of Salthill, about 2 miles from Galway. 



A minor bar is well seen from the railway on leaving Oranmore station on the 

 way to Galway. The till cliff of Eoscarn Point is there seen opposed to a similar 

 cliff on the opposite side with a channel cut between them. 



If the ancient barrier was nearly as high as the present cliffs of Barna, the 

 waters of the traditionary lake must have backed over a large area of the flat land 

 around Galway, and it may even have been continuous with Lough Corrib. 



Another form of drift which covers a large area of the central limestone plain 

 of Ireland is described as analogous to that which covers the Dovrefjeld, the Fille- 

 fjeld, and most of the other Norwegian fjelds, and which the author has described 

 in detail in 'Through Norway with Ladies,' pages 50 and 238, as the material 

 which subsided when the great neve of the Great Ice Age finally thawed away. 

 It is neither boulder clay nor loose stony moraine material, but an intermediate 

 agglomeration of sand and gravel with boulders that are more angular than those 

 of moraines or boulder clay, and show little or no signs of striation. The name of 

 boulder sand or glacier gravel is suggested. It occurs, commonly as a thin 

 layer spreading over the limestone and occasionally as long humpy ridges, and 

 is connected with the formation of Eskers. 



1878. M M 



