86 ME. A. C. NICHOLSON ON HIGH-LEVEL 



8. High-Level Glacial Gravels, Gloppa, Ctrn-y-bwch, near 

 OswESTET. By A. C. Nicholson, Esq. (Read December 9, 

 1891.) 



[Communicated by "Wm. Shone, Esq., F.G.S.] 



The Gloppa (spelt ' Glopa ' on the Ordnance map) is a small farm, 

 about two miles north-east of Oswestry, situate on the eastern slope 

 of the ridge of Carboniferous rocks (Millstone Grit) which forms 

 the western boundary of the Northern Shropshire and Cheshire 

 Plain, and upon this and adjacent farms the gravels and sands 

 are spread out. The main mass is comprised in a ridge of eskers 

 about 1000 yards long, and appears to rest immediately upon the 

 Millstone Grit, the beds of which formation crop out directly 

 to the westward, and dip here about 20° to 25° E. and S.E., the 

 average slope of the hill being about 10°. The portion of the 

 deposit worked out forms but a small part of the whole, although 

 about 33,000 tons of material have now been extracted. 



A pit was opened here in the year 1888 for the purpose of 

 getting sand for the filter-beds on the Oswestry works of the 

 Liverpool Yyrnwy Waterworks, and since that date I have had it 

 under observation ; it is not now being worked. 



The deposit ranges here from about 900 to 1160 feet above sea- 

 level, but the main mass is from 1000 to 1150 feet, the sandpit 

 worked being 1070 to 1130 feet. The highest point at which I 

 have found marine shells in the drift is 1120 feet; the other 

 recorded instances of such drift at similar heights in Great Britain 

 being Moel Tryfaen (1330 to 1360 feet), Prestwich's Patch, 

 Macclesfield (1150 feet); and in Ireland there is Three Eock 

 Mountain (1100 to 1200 feet). I have noted similar gravel on 

 Selattyn Hill, two miles to the north along the Millstone Grit ridge, 

 at a height of 1250 to 1300 feet, but found no shells at that locality, 

 there being but a small exposure a few feet deep. Similar 

 deposits occur at various points along the Millstone Grit ridge, 

 such as Erondeg and Halkyn, and have been noticed by the late 

 D. Mackintosh and others. 



Nearer Oswestry, but at much lower levels (400 to 550 feet), 

 occur a series of eskers of somewhat similar character, as at Old 

 Oswestry gravel-pit, but these are undoubtedly of more local origin, 

 although they contain a large admixture of northern erratics. 

 These have been described by the late D. C. Davies in the Proc. 

 Geol. Assoe.^ In the same paper Mr. Davies gave two sections, 

 figs. 10 and 11, on the Oswestry Eacecourse, evidently parts of 

 the Gloppa deposit as shown in some old pits long since closed. 



The greatest depth exposed at Gloppa has been about 60 feet ; 

 the base has not been reached, but it is hardly probable that the 



^ Yol. iv. (1875) part vii. ; see figs. 8 and 9. 



