of the Scratched Rock Surfaces. Aa 
stood at least 600 feet higher than at present. Any shells 
of this period, at the lower levels, will be found deeply buried 
under later deposits, while at the meter levels they he 
exposed. 
_ (2.) and (8.) The clays and sands, and their accompany- 
ing shell-bed marked @ belong to the later period, when 
the sea-level had fallen 400 feet. The higher levels being 
by this elevation of the land protruded above the sea, the 
shell-beds already found on them were preserved from being 
buried under later deposits. None of the later shell-beds 
are therefore to be found at this elevation, but they present 
themselves at the lower levels, at or near the surface, among 
the later clays and sands. 
II. We now come to the second or post-glacial group of 
deposits —(1.) The first member of which is the later shell- 
clay to which we adverted above. Like the marl, it is de- 
rived from disintegrated Silurian strata, but more especially 
from the clay schists of that age. When freshly dug out, it 
is generally of a bluish-grey colour, and less wet than the 
marl. It has been deposited in salt water, and very often 
contains well-preserved shells of the same species as are 
still living on our coasts. In position it is superior to the 
marl and glacial sand ; but it does not rise to so high a level 
above the sea as these, its maximum height being about 
300 feet. In general, it does not ascend above 250 or 270 
feet. This shell-clay is sometimes, though not always, 
mixed with lime. It is frequently worked for bricks. 
(2.) The brick-clay in the marine beds is identical with 
the inland clays of the higher levels, from which it only 
differs in the greater thickness and purity of the banks in 
which it presents itself. It is generally blue or brown in 
colour, and these shades sometimes alternate in clods or 
stripes. No shells are found in the brick-clay. 
In the course of the valleys this clay is found at all eleva- 
tions deposited in old lake basins; it disappears, however, 
in proportion as we advance into the quartzose districts. 
Above the old sea-level it is very often mixed with sand, 
and contains layers, more or less thick, of fine sand. Since 
even at the lower levels it contains no shells, we must infer 
