Chaklesworth — Glacial Geology of North- West of Ir-eland. 295 



This great deposit is quite flat/ save for some depressions wliich, usually 

 mall and filled with water, and ou the whole singularly few in number, stud 

 the surface in certain parts, e.g.. Lough Enagh Eastern,^ and two or three 

 smaller ones in this immediate neighbourhood (N". of Londonderry), and 

 those which occur as far east as Limavady and along the valley of the 

 Faughan to near Drumahoe. Though the height of the terrace at this locality 

 is about 120 feet, O.D., it falls gradually down the valleys, attaining over the 

 greater part of its area an altitude of roughly 50 feet above sea-level. 



A very good section, exceeding 20 feet in depth, occurs near tlie roadside 

 at Stradreagh, where tlie deposit is seen to consist of stratified and well 

 water- worn sands and gravels, in places current-bedded and calcreted. The 

 pebbles include all the rocks found in the drift of the country to the south. 

 At Faughan Bridge and a few other places shingly accumulations of similar 

 material suggest by their nature and their current-bedding (from the south) 

 deposition by powerful currents issuing from the Faughan and other valleys. 

 Various opinions on the origin of this very extensive terrace have been 

 expressed. In the Geological Survey Memoir, descriptive of the Limavady 

 area, the following passage occurs^ : — 



" It [the terrace] has been sometimes regarded as a recent raised 

 beach. A little examination, however, shows that this is not the case, 

 as its contents are precisely similar to those of the gravel terraces 

 above it, and differ widely from those in the raised beach." 



With this view of the nature of the deposit and its non-marine origin— shells 

 are entirely absent, though present in considerable quantities in the raised 

 beach — I am in complete agreeraent. Its glacial or late-glacial origin would 

 seem indeed to be beyond question, as was recognized by J. E. Kilroe, whose 

 view on its mode of formation is expressed as follows^ ; — 



"The materials have obviously been distributed by flood waters 

 issuing from receding glaciers over the valley floor and the low ground 

 bordering the coast during the final disappearance of the permanent 

 ice from the region." 



He finds support for this view in the existence of kettle-holes. 



This theory of the origin of the great gravel spread is consistent with 



' This is especially well seen in the bay of Eglinton and in the stretch to the west of 

 the Londonderry-Limavady road. 



^ A photograph of one of these depressions is given in the Londonderry Memoir 

 (1908, PL VI, facing p. 60). 



' Sheet 12, p. 26. •> Londonderry Memoir, p. 60. 



