924 TSM lety (CH Eaneno== 
between the gravels and the boulder-clay. Most of this high ground, 
in fact, has little boulder-clay upon it, and probably any such deposit 
was originally thin and irregular in its distribution, and has been 
largely washed away by rain. 
, Boppam Den. 
Towards the east end of the Buchan Ridge, about a mile and a half 
south-west of Buchan Ness and a mile north of Longhaven Station, 
a remarkable dry valley runs northwards across the granite hill. 
It is about 70 feet deep, and is occupied by only an insignificant 
streamlet; the floor of the valley is covered with peat, and its 
northern half is converted into a lake by means of an artificial 
dam. The course of the channel is at first north-east, then north, 
and it opens into flat country at each end. 
As pointed out by Dr. Bremner, it is undoubtedly a temporary 
glacial channel, by which melt water from ice sheets has escaped 
across the ridge. On both sides of the valley the slopes are steep, 
and on the west side are covered by flint gravel; on the east side 
also the gravel occurs, but towards the north end of the channel 
granite crops out on the eastern slope. Many small pits have been 
opened in the flint gravel, and on the banks of the reservoir the 
waves have cut good sections 10 feet or less in height. An 
examination of these shows that the gravelis not washed by stream | 
action. There are no sandy layers, bedding, or current bedding 
such as are usual in materials deposited by glacial outwash, and 1t 
is entirely different in character and composition from the glacial 
gravels of this district. The surface characters are in some measure 
affected by rainwash and soil slips from above, but a small pit which 
we dug for about. 2 feet at the north-east end of the dam exposed 
true flint gravel with yellowish and white fine plastic clayey sand 
as matrix, exactly similar to the deposits at Hillside of Aldie, 
Mountpleasant, Delgaty, and Windyhills described above. The 
pebbles are perhaps 90 per cent of flint; the remainder are the 
quartzites typical of these deposits. The characters, in fact, are 
_ those of undisturbed Tertiary beds. 
A careful scrutiny of the exposure at the locality mentioned 
showed that this gravel is overlain by reddish tough boulder-clay, con- 
taining pink felspars and fragments of the Peterhead granite, which 
isthe country rock. The gravel, we hold, islying ina valley originally 
cut in the Tertiary platform, filled up by the flint gravel and 
re-excavated at the close of the glacial period. The coincidence 
seems remarkable, but it may be suggested that the presence of a 
gravel-filled hollow would probably determine the situation of the 
glacial overflow channel by the rapid deepening of any stream- 
course which happened to coincide with it. This patch of flint 
gravel apparently marks the eastern end of the Tertiary deposits 
preserved in this district. 
1 A, Bremner, op. cit., p. 339. 
