Geological Society of London. 181 
Tsles, during which time the climate was milder than at present, and 
big trees flourished where now they will not grow. 4th, subsidence 
to the present level, the submersion of the peat and forest-beds, the 
laying down of tidal silt upon them, and the accumulation of blown 
sand along the sea-margin extending to a considerable distance in 
an inland direction. 
It was estimated, from a variety of considerations, that these 
events, all posterior to the Glacial period, represent a lapse of time 
of not less than 57,500 years allotted as follows :—40,000 years for 
the elevation succeeding the Glacial period measured by the denu- 
dation of the Boulder-clay in the valleys, 15,000 years for the 
accumulation of the estuarine silts, clays, peat, and forest beds, and 
2500 years for the blown sand. 
2. “Note on the Movement of Scree-Material.” By Charles 
Davison, Esq., M.A. Communicated by Prof. T. G. Bonney, D.Sc., 
LL.D., F.B.S., F.G.S. 
The author noticed the frequent high angle of slope of screes, 
and called attention to Canon Moseley’s observations on the down- 
ward creep of lead on the roof of Bristol Cathedral, and his sub- 
sequent experiment, and stated his belief that stones free to move on 
the surface of a scree must be affected in the same manner. This 
he proved by experiments, the result of which he described. 
These experiments showed that stones do move downwards, owing 
to alternate contraction and expansion, the movements accompanying 
or occurring a short time after the change of temperature, that the 
descent is greatest on days of bright sunshine interrupted frequently 
by passing clouds, and that rain slightly increases the rate of descent. 
A description was given of a scree on Hindscarth, Cumberland, 
in which the stones lie with their longer axes pointing down the 
slope; and it was pointed out that the movement of the stones in 
the way described would cause the surface-stones to fall off those 
on which they rested, and that others would be dislodged during 
their descent. A numerical estimate was then made of the total 
amount of movement produced on a scree of a certain size by ex- 
pansion and contraction of the surface-stones, and after alluding to 
the relative efficiency of this and other agents upon various screes, 
the author concluded by pointing out that in the case of the moon 
this might be almost the only agent at work. 
3. “On some Additional Occurrences of Tachylyte.” By Grenville 
A. J. Cole, Hsq., F.G.S. 
An intrusive sheet, some eight feet thick, among the basalts of 
Ardtun Head in Mull, has selvages of tachylyte. The specific 
eravity of the glass is 2°83, and in other respects it resembles the 
examples already described from the west of Scotland. But in thin 
section, numerous fairly translucent spherulites are seen, which 
accumulate towards the inner part of the selvage until the glassy 
material between them disappears, and they become polygonal by 
contact. The rays of these spherulites are often alternately grouped 
in brown or greyer bundles, both series exhibiting striking pleo- 
chroism; but the brown fibres appear darkest when their longer 
