to the north, and southern forms advanced. So, when we try 
to correlate glacial beds in England with those elsewhere, we 
must not too hastily assume that the regions characterized by 
certain forms were defined by the same boundaries as now 
hold good. 
The downward movement carried down the land to far 
below the level at which it stands at present, and since that it 
has been coming up again with oscillations. Now, we must 
inquire in greater detail into the evidence. 
What was the greatest height to which it rose in Glacial 
times we have not evidence to prove. But we can show a 
depth to which at least it must have sunk after the Glacial 
times. 
On the western spurs of Snowdon, in a trough between 
Moel Tryfaen and the hills, there is a bed of sand and loam in 
which are whole and broken shells, most of them species found 
upon the coast to-day. With them are stones such as are 
found in the drift about, not much water- worn ; some even 
retaining the glacial scratches ; and, perhaps, most interesting 
of all, there are not uncommonly flints such as occur in gravel- 
beds in east and southern England, — sub-angular, ferruginous, 
some more, and some less rolled. 
We will make these beds a central point around which we 
will collect our evidence. They have been noticed by Trimmer,* 
Darbishire, f Lyell, J Ramsay, § and many others. They are well- 
known, and all the leading facts are well-established. First, 
as to its height above the sea. The bed in which the shells 
are found, according to Ramsay, runs up to 1,170 feet, || but 
Ramsay holds that beds precisely similar, and to be bracketed 
with them, but which have not yet yielded shells, run up to 
heights of 1,800 feet or more on the same mountain group. 
At Macclesfield, If near Manchester, another bed like it, and 
containing mostly the same shells, was found by Prestwich at 
1,250 feet above sea level, and near Congleton** Ramsay 
records another at 600 feet. From the time when the moun- 
tains of that district were so high that glacier ice crept down 
them, to the time when all the land went down from 1,200 to 
1,400 feet below its present level, must surely have been an 
* Proc. Geol. Soc., vol. i., p. 331. 
t Proc. Manchester Lit. Phil. Soc., 1863-4, p. 177. 
X Ant. Man , p. 315. § Phys. Geol., &c., p. 413. 
|| Darbishire estimated the highest point from which he obtained shells at 
1,370 feet. IF Darbishire, Geol. Mag., vol. ii., p. 192. 
** Ramsay, Phys. Geol., &c., p. 413. 
