290 
YORKSHIRE DRIFTS. 
layers of sand and gravel. The third division, comprising the 
hillocks and terraces of unstratified matter, Mr. Clay considered may 
be true moraines, left by the glaciers as they retreated before the 
increased temperature attendant upon the gradual elevation of land, 
and in this way the appearances enumerated may have resulted from 
the same general cause. 
Early in the following year, j\Ir. Thomas Sopwith, of Newcastle, 
read a paper before the Society on the evidences of the former 
existence of glaciers in Great Britain. He traced, in a most forcible 
manner, the extension of glaciers from the Highlands of Scotland, 
the Cambrian mountains, and those of Wales, into every valley near 
them, and over a much further extent of country than had hitherto 
been known. He described the action of existing glaciers in Switzer- 
land, the formation of lateral and terminal moraines, instanced the 
scratching of the surface over which the glacier passed, and the 
striation of the boulders torn from the rocks in its passage, and 
gave instances of similar results existing in the North of England, 
which he attributed to the same cause, and showed the rapid 
strides which had been made in a short time in the acceptance of the 
glacial theory. 
At the meeting of the Society held in June, 1851, at Sheffield, a 
paper was read by ^Ir. H. C. Sorby, on the contorted Stratification 
of the Drifts of the Coast of Yorkshire. Sir Charles Lyell had com- 
municated a paper to the Geological Society in 1840, on Contorted 
Stratifications of the Drifts. Since that time a paper had been read 
by Mr. Trimmer, in which he attempted to explain these phenomena 
by supposing that masses of ice had been fixed amongst the beds 
when they were deposited, and that on these subsequently thawing, 
the strata sunk down into the space they occupied, Ly ell's opinion 
being that they were due to stranded icebergs. Mr. Sorby considered 
that the contortions were probably due to both these causes, for, in 
some instances, the contorted strata occupied a ver}^ limited area, and 
the underlying and superimposed strata were laid horizontally above 
and below. This could only be due to a large mass of ice becoming 
embedded in the boulder-clays as they were deposited, which sub- 
sequently thawed, and the space became filled up with masses of sand 
