550 
Proceedings of the Royal Society 
Monday , Ylth May 1869. 
Professor KELLAND, Vice-President, in the Chair. 
The following Communications were read : — 
1. On the Basin of the Firth of Forth, and some of its 
Geological Phenomena. By David Milne- Home, Esq. 
I. An account was given of the dimensions of the estuary, in 
respect of length, width, and depth ; and also of the general direc- 
tion of the axis of the estuary. 
II. It was next shown that the formation of the estuary was 
probably due to the great geological fractures and dislocations 
which had taken place in this part of Scotland, inasmuch as the 
direction of these was parallel, or nearly so, to the axis of the 
estuary, and as the downcasts in the adjoining counties on the 
north and the south were all towards the estuary, thus producing 
a trough or valley, deep enough to be entered and filled by the 
sea. 
III. The author, before describing the newer deposits filling the 
basin of the Frith of Forth and covering its adjoining shores, 
stated that the materials of these deposits were most probably 
derived from the upcast strata which, along the slips and fractures, 
had formed high exposed cliffs, and which yielded to the influence 
of tbe sea, if the sea covered them, or atmospheric changes, if they 
were above the sea-level. 
1. There were no data for determining when these dislocations 
took place. There was clear evidence, however, that in the 
Western Highlands there had been outbursts of trap at a period 
later than the chalk ; and Mr Cumming thought, that in the Isle of 
Man part of the boulder-clay had been formed after great disloca- 
tions there. 
2. An account was then given of the various kinds of deposits, 
chiefly by means of reports obtained of borings, which showed the 
layers of clay, sand, and gravel passed through, with the thickness 
of each. 
