612 LIEUT.-COL. H. H. GODWIN-AUSTEN ON THE 
to the Drift, Sir Roderick Murchison repeats “. . . in some cases 
the old drift has been carried wp the present valleys.” I do not 
agree with Sir Roderick Murchison as regards the vast volumes of 
moving water occupying the valleys, although lakes may very 
possibly have been formed for a time in such positions as the Pease 
Marsh, or from Petteridge downward on the Mole drainage. Yet 
in this paper all his excellent observations and the facts are brought 
before us; and I would emphasize the transit of material to which he 
refers by adding that the drift was invariably from north to south 
all along the line of the North Downs from Kent to Farnham, and 
that on the elevated ridge of Leith Hill, also subject to like cold 
conditions, the local transport of drift was down its northern slope 
towards the main valley. 
What would be the effect of a reduction of the mean annual tem- 
perature on this undulating flat country? There would be an ex- 
cessive snow-fall in winter which would accumulate to a great depth, 
with much drift-ice in the streams and rivers. It is not necessary 
to suppose any thing of the nature of a glacier as we know them in 
Alpine regions ; but what would result, if the cold were great enough, 
would be the formation of frozen snow-beds on the higher grounds 
lasting through the heats of summer, and such would be the exact 
counterparts of those patches of ice, many square acres in extent, 
that are to be seen at the present day on the wide level plateaux of 
the Chang Chingmo in Thibet—that is to say, solid ice not more than 
20 feet thick, with a flat but much broken surface and with a wall-like 
margin in most places. These I noticed lasted until the winter snows 
began again, and in very warm summers they may almost entirely 
disappear. A very slight lowering of the annual temperature would 
soon cause these thin ice-sheets to thicken and extend on all sides. 
Such, I conceive, was very much the state of all our high 
grounds in the south of England at the time of the Drift deposits, 
when in parts of Scotland, the north of England, and Wales glaciers 
of considerable size existed and erratics were carried south. Such 
snow and such frozen snow-beds wouid have quite a sufficient force 
to act on the surface of the country, wearing it down to the even — 
beautiful curves 1t now presents, and distributing the waste over 
the adjacent lower lands. In summer the streams would have been 
in a state of extreme flood, transporting much larger material than now 
down their courses, and distributing it further from its source. 
Supposing the existence of any sort of obstruction in the gorge of 
the Wey, it might be by ice or by change of level, drift or detritus 
from the Chalk would thus extend into the Pease Marsh and Tilling- 
bourne, Mole, &c. On the north face of the downs these conditions 
may have béen combined with the proximity of an arm of the sea 
and coast-ice, as put forward by Mr. Godwin-Austen*. The ques- 
tion of relative age, as compared with similar deposits elsewhere 
in the south of England, such as the former sea-beaches of Brighton 
and Folkestone, and the valley-gravels of Chichester and the Medway, 
© eerent. pa. 
