CLARK i GLACIAL SECTIONS. 
425 
vertical, line separated this from beds of boulder clay, not so sandy 
and full of ice-scratched pebbles but containing- some boulders. 
The new Foss Islands branch of the N.E.R. exposed some 
interesting- sections ; and here, best of anywhere, was seen the 
junction of brick-earths and glacial beds. The Foss Islands are 
a marshy spot, where the stream of that name receives the Tang 
Hall Beck. So inaccessible was the city at this point that no 
artificial defence was ever erected. The peat and clay, where 
their surface is lowest, are 9 to 12 feet deep, resting on sands and 
gravels, probably glacial. These must be about 5 feet below the 
present Ouse level, or not 20 feet above the sea. The brick-clays, 
however, rise considerably at the sides of the beck, biing 30 or 
35 feet thick where worked on the south ( Walmgate) side. Here 
they rise about 20 feet above the Marsh, as well as on the north 
(Laperthorp) side, (Plate XXIII., Fig. 1, F.), where the junction 
above mentioned was exposed by cuttings about 1 2 feet in depth. 
The stiff boulder clays had first been denuded by strong currents, 
leaving an irregular surface. This, at least in the part cut through, 
had been next covered with sand. Most of this, with the upper 
part of the boulder clay, appear next to have been planed away 
by some gentler denudation, and above the nearly level surface so 
produced, averaging seven feet above the rails, lay warpy brick- 
earths. Thus we get lenticular masses of sand, plano-convex in 
shape, lying between the two kinds" of clay. Whilst the works 
were in progress the contrast between them was very great, the 
lower layer being left with a rough slope, whilst the upper was 
worked in a series of miniature terraces. 
At places the boulder clays rose higher, even forming a 
tumulus-like boss east of the Heworth road. Great expectations 
were centred upon the cutting of this by our friends the anti- 
quarians, who had its probable history already prepared. But 
the navigator's spade, relentless as fate, shattered these baseless 
fabrics in proving, once more, that even the slightest of York's 
little eminences may be due to glacial beds. 
