D. MACKINTOSH ON HIGH-LEVEL MARINE DRIFTS. 359 



ditcd the process of rounding stones; so that in the case of the 

 summit of this mountain (which is situated at a lower level than 

 that of the gravel and sand on Moel Tryfan, Frondeg, Macclesfield 

 Forest, &c.) it is not necessary to suppose that the land subsided 

 more slowly than at the levels immediately below and above, so as 

 to afford more time for elaborating rounded gravel and sand. As 

 already hinted, the scarcity of shell-fragments accords with the 

 idea that the rate of submergence was not sufficiently slow to allow 

 much time for the growth and accumulation of Mollusca. It ought 

 likewise to be stated that on many parts of the mountain the stones 

 in the gravel-beds are not much rounded. 



IV. Discovery oe High-level Deposits of Gravel and Sand 



BETWEEN MlNERA AND LLANGOLLEN YaLE, DENBIGHSHIRE. 



For a long time, while travelling by railway between "Wrexham 

 and Euabon, I fancied, from the surface- configuration of the eastern 

 or outer slope of the range of mountains between Minora and Llan- 

 gollen vale, that marine gravel might there be found at about the 

 same height as on Moel Tryfan ; but, being then bent on finding 

 sea-shells at higher levels than the Moel-Tryfan deposits, I did not 

 explore the district until near the close of last year (1880). From 

 the railway, for some distance westward, the ground is flat or gently 

 undulating, with an average elevation of between 300 and 500 feet. 

 In many places sand may be found under a deposit which is hori- 

 zontally continuous with the upper Boulder-clay of Cheshire ; and 

 here and there the sand, graduating into gravel, rises in the form 

 of mounds or knolls. From the commencement of the gradual rise 

 of the ground in a westerly direction up to about 1000 feet the pre- 

 vailing drift is a clay or loam, with angular stones and large Carbo- 

 niferous-grit boulders from the mountain-range above mentioned. 

 At about 1000 feet the ground rather suddenly rises, and the stones 

 (as may be seen in ploughed fields &c.) become more or less rounded. 

 A little west of Braich, in the district called Frondeg (see 1-inch 

 Ordnance map), the ground abruptly swells into a series of ridges 

 and hillocks, which consist of well-rounded gravel and sand. 



1. Surface-configuration and Character of the Deposits. — In the 

 Frondeg district the gravel and sand knolls, with intervening or ad- 

 jacent deposits of a similar character, extend for about a mile and 

 a half from north to south, and about one third of a mile in breadth 

 from east to west ; but as similar accumulations are repeated at inter- 

 vals as far south as Mountain Lodge, the whole length of the deposits 

 may be about three miles — that is, supposing they extend no further 

 south. On walking from Braich to the summit of the mountain-range 

 in a westerly direction, after passing the gravel mounds, the surface 

 becomes very flat and covered with peat. The breadth of the flat 

 (which in some places extends, with a very gentle ascent, as far as 

 the summit of the ridge, in other places not quite so far) is about 

 half a mile. So far as can be seen in brook-channels, the peat 

 overlies a deposit of clay with angular stones and large angular 



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