Vol. 58. | GLACIER-LAKES IN THE CLEVELAND HILLS. 487 
conveniently be taken as typical of this feature also. Above Rain- 
dale Mill several tributary streams come in, but they are all very short 
and of small volume, and it is clear that the main valley could not 
have been produced by confluence of such elements ; moreover, they 
enter the main valley with a plunging slope, almost every one pro- 
ducing waterfalls, and sometimes sheer drops. They come out on the 
flat moor-tops 300 feet above the main valley, a few hundred yards 
above the confluence. It is right to point out that, for a considerable 
distance, the moor is a plateau corresponding with the top of a hard 
bed of rock (Kellaways), and therefore the small streams would find 
it difficult to cut through; but this condition is not general, while 
the peculiarity of the lateral valleys is. 
An alternative possibility which I have had also to keep constantly 
in view is, that in limestone-rocks streamless valleys may occur 
which have been produced by normal drainage during the Glacial 
Period (when all rocks were frozen, and therefore impervious to 
water), whereas now no streams are possible in consequence of the 
porosity of the limestone. Such valleys I know well; they abound 
on the Chalk Wolds, but their characters are quite different from 
those of Glacial overflows: they do not cut watersheds. 
V. Pre-GuactAL LEVEL oF THE LAND. 
The pre-Glacial level of Yorkshire appears to have been consider- 
ably above its present elevation, for borings and mine-workings have 
proved in many places Drift-filled hollows descending far below sea- 
level; yet in no case has anything like a sea-bottom or marine 
deposit been encountered, except in Holderness, to which reference 
will be made later. 
Borings close to the coast prove nothing very definitely, as we 
do not know the exact form of the pre-Glacial coastline ; so that the 
borings near the mouth of the Tees, stated by Mr. Barrow ! to prove 
Drift down to 90 feet below sea-level, do not yield much enlighten- 
ment on this particular point ; and the borehole at the Grand Hotel, 
Scarborough, which proved the presence of Boulder-Clay to a depth 
of 100 feet below sea-level,” may well have been outside the pre- 
Glacial shore-line. Right down the great valley from Newcastle to 
Doncaster, however, there is abundant evidence of a convincing kind. 
The great wash along the Leam depression described by Nicholas 
Wood & E. F. Boyd” is an old river-valley, Drift-filled at present, 
which at Gateshead is 140 feet below sea-level. 
From the Tees southward, borings indicate a great depth of 
Drift, until a line connecting Northallerton and Bedale is reached. 
Here the Drift is shown by boreholes at Northallerton, Thornton-le- 
Moor, Leeming Lane, and other places to be very thin; and, as it 
1 Mem. Geol. Surv. ‘ North Cleveland’ 1888, p. 68. 
2 Mem. Geol. Surv. ‘Oolitic & Cret. Rocks South of Scarborough’ 1880, p. 31. 
3 Trans. N. of Engl. Inst. Min. Eng, vol. xiii (1865-64) p. 69. 
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