34 



have come into action. The other members of the Tertiaries 

 had been deposited in quiet lakes, estuaries, or seas, with 

 mud and sand, and shingle, derived from lands adjoining 

 them, and enjoying a warm climate, but a tremendous change 

 must have ensued at the close of the Pliocene period in respect 

 of climate, probably due to a great change in the distribution 

 of land and water in both Europe and North America. It was 

 shown that a depression of the whole surface of this island 

 must have taken place, till the depth of at least 2,000 feet 

 below the sea was reached ; that during this probably gradual 

 fall and equally gradual rise again, an enormous amount of 

 denudation of the rocky beds must have taken place, partly 

 from the action of land ice in glaciers, but mainly from the 

 much greater energy of the ice-fields and bergs, which must 

 have been at work at this period, just as they are now in both 

 high northern and southern latitudes, grinding down and 

 cutting through submerged lands, over which they are driven 

 by strong sea currents, and as they melt or overturn, throw- 

 ing down the load of rocks, clay, and sand with which they 

 are freighted, to mix in a heterogeneous way with the mud bed 

 already formed by the grinding action of the ice, both land 

 and sea. In the upward movement of the land there seems 

 to have been pauses from time to time of very lengthened 

 periods. Some of these can still be plainly recognised by the 

 continuous lines of eskers or old sea margins, which are very 

 remarkably preserved in the great central limestone district 

 of Ireland, sometimes only faintly indicated by a shallow 

 bench or terrace on a steep hill-side ; sometimes by a line of 

 old sea-caves, as in our own locality, and the last line of eleva- 

 tion is familiar to most, in the cliff which lends such a 

 picturesque charm to the margin of our Lough, and can be 

 traced around the shores of the British Islands at a height of 

 about twenty-five feet above present sea-level. In conclusion, 

 it was shown that this theory, as now briefly explained 

 supplied a solution to the following difficulties: — 1. The 



