Kinahan — On Gravel Terraces. 637 



as the winters become less cold, the summer less warm, and the 

 rain-fall greater, the ice in the bays would gradually disappear, 

 while as the evaporation was less, the hollows would become lakes, 

 thus accounting for the " breaking forth " of the different inland 

 and sea loughs. 1 This digression, although it may have a certain 

 interest, does not seem to account for the great difference in the 

 features of the marginal slopes of the valleys of Loughs Swilly and 

 Foyle ; but during a recent traverse of western Tyrone and Fer- 

 managh it occurred to me that the phenomena in connection with 

 the latter may possibly be explained by what is found at the 

 present time in the river valleys of the "Foot Hills" of the 

 Canadian Rockies. 



Let us suppose that when the climatic conditions of Ulster were 

 more or less similar to those of Canada at the present day, the 

 Silurian hills (Loicer Old Red Sandstone type) east of the plain of 

 the Loughs Erne, and extending eastward nearly to Cookstown 

 (which for convenience sake may be called the " Fintona moun- 

 tains," after the town nearly in their centre), was a snow-field 

 feeding small glaciers in the upper portion of each valley, while in 

 each valley there was a river thick with silt and sand, each also 

 being margined by gravel terraces. This may be seen at the 

 present day in the upper portions of Bow and Belly rivers, Alberta, 

 and in other river valleys east and west of the Canadian Rockies. 



Many circumstances in connection with the surroundings of the 

 " Fintona mountains " seem to support such suggestions. To the 

 westward in the low country of the Loughs Erne the gravels seem 

 to partake more of the character of glacial than marine accumu- 

 lations; at the "divide," Pomeroy, in the central east and west 

 valley, there is an excessive accumulation of sand and gravel, as at 

 the "divides" of the river valleys in the Rockies between two 

 glacial rivers or valleys ; while the gravel terraces along the slopes 

 and the flats of the Strule, Mourne, and Foyle valleys, if we allow 

 for the subsequent modification due to meteoric denudations, are 

 very similar to those of the Bow river, Alberta. 



The genesis of these terraces in the valleys of the rivers of the 



1 Some lakes may have "broken forth," on account of a change in the level of 

 the land, as I have elsewhere suggested, giving reasons in connexion with Galway Bay 

 and Lough Corrib, 



