546 James Durham—Pleistocene Geology, Firth of Tay. 
of 500 feet high. which has on its north-west side, near the top, a 
layer of till partly composed of finely ground red sandstone of the 
neighbourhood and partly of a dark clay derived from the dolerite of 
the hill, with the usual admixture of angular and smoothed stones, 
while the projecting parts of the rock are smoothed from below 
upwards. Similar testimony to the thickness of the ice so close to 
the sea is borne by the neighbouring hills, though none of them are 
quite so high as the Law. 
A very remarkable feature of the low grounds in the neighbour- 
hood of the Firth of Tay is a great and far-extending raised plain or 
terrace, composed of well-stratified sand and gravel; the fine even 
layers of sand show that it must have been laid down in the tranquil 
depths of the sea; it is largely composed of stones foreign to the 
immediate neighbourhood, its flat top is exactly 100 feet above the 
datum-line and is usually known as the 100-feet terrace; it fringes 
the hills over which the ice has flowed, but its even stratification 
from top to bottom affords undoubted evidence that at the time of its 
deposition the ice had disappeared from the shore and at the time of 
the disappearance of the ice that the land was submerged upwards 
of 100 feet. 
Thus as we found that the first great depression of the land took 
place during a temporary recession of the ice, this depression oc- 
curred when the glaciers were in their final retreat. 
As the glaciers disappeared, they must have left the land strewn 
with morainic débris; a very large proportion of this matter would 
he more or less rapidly swept into the sea by torrents of water from 
the melting ice, and great swollen rivers, and spread over its bottom, 
which explains why the constituents of the terrace are nearly all 
rocks of more or less distant origin. 
After this vast load of material was deposited in the sea, a great 
elevation took place, the land and a great part of the sea-bottom 
being raised to a considerably greater height than at present, which 
is shown by a more recent formation than the terrace usually known 
as the “submerged forest” or “peat” bed. This consists of a bed 
of bluish sandy clay, imbedded in which are numerous trunks, 
branches, and twigs of trees, along with leaves and nuts, occasionally 
bones of deer are met with as well as fragments of insects, all 
characteristic of a luxuriant forest growth, which would not likely 
thrive just at the sea-level. This bed in the Firth of Tay is found 
between high- and low-water limits, and passes below the latter. 
This forest bed is in turn overlain by a considerable thickness of 
sand and clay, evenly stratified, and evidently deposited in’ water of 
some depth, so that after the forest period, during which the climate 
appears to have been very much as it is now, the land was again 
submerged, from which depression it is possibly at the present 
moment slowly recovering. 
From the foregoing it seems evident (1) that throughout the first 
maximum extension of the ice-sheet the Jand stood at least as high 
as at present; (2) that after the ice had disappeared, or at least 
withdrawn, from the sea-shore, the great submergence of 500 feet 
