358 



D. MACKINTOSH ON HIGH-LEVEL MARINE DRIFTS. 



of gravel and sand on its summit could never have been accumulated 

 by the action of fresh water flowing onto it from a higher level. The 

 mounds range from about 750 to about 900 feet above the sea. The 

 rounded stones they contain are chiefly local limestone and grit of 

 Carboniferous age ; but Eskdale granite and Lake-District felstone 

 may be found in some places, and chalk flints may occasionally be 

 seen. The most striking mounds in which excavations have exposed 

 sections are one situated near Brynford (not far from Holywell) 

 and another towards the S.E. end of the mountain. The latter is 

 named Moel-y-Crio on the Ordnance map, and rises from the 

 summit of a ridge about 950 feet above the sea, with ground falling 

 all around it, except on one side, where for some distance it is 

 nearly horizontal, and then falls to a lower level. It would appear 

 to have been accumulated not so much by wave-action as by the 

 piling agency of sea-currents while meeting or parting. 



Pig. 2. — Perched Gravel-mound on HcdTcin Mountain. 



The Halkin-Mountain deposits of gravel and sand occur at a 

 lower level than the other high-level marine drifts described in this 

 paper ; and they are not very distinctly separated (excepting, in 

 most places, along the east side) from the low-level gravel and sand, 

 which extends upwards from the sea-coast, and inland along the pass 

 between Mold and Bodfari, which is traversed by the Chester and 

 Denbigh Kailway. Exceedingly few shell-fragments have been 

 found in the gravel and sand of Halkin Mountain ; but its compara- 

 tively flat summit, in places surrounded by ridges, must have been 

 very favourable to the accumulation of rock -fragments derived from 

 the inner slopes of the ridges ; while it is easy to understand that 

 these fragments, instead of being washed down the mountain-sides 

 into deep water, would remain for a considerable time at the mercy 

 of sea-waves, so as to become more or less rounded and smoothed by 

 attrition. It ought likewise to be remembered that the mountain, 

 while an island, must have been exposed all round its coasts to 

 winds, which, by increasing the power of breakers, may have expe- 



