of the Scratched Rock Surfaces. 9 
produced’ by the presence of a larger quantity of lime than 
usual ; but they are much more probably fragments of the 
Silurian limestones, rubbed and worn to their present shape 
during the ice period, by the same agency as broke and 
scoured and polished and crushed and rubbed all the surface 
of our rocks, and so prepared the stores of debris that form 
our boulder-clay. Such rounded lumps or balls are the dis- 
tinctive characteristic by which to recognise this marl. 
The marl often contains also extremely thin and small 
scales of mica, which glitter in the sun,——a proof how slowly 
this marly clay was deposited, and how still the water in 
which it was allowed to sink. It was only when they 
came to rest in the bosom of the deep and quiet ocean that 
the mud-laden waters which poured from the inland ice 
could part with their burden; and in harmony with this we 
find, that the maximum height at which this marl is found 
is 400 feet above the present sea-level, a height which, as 
we shall see, corresponds exactly with that of the older 
marine shell-beds—[both facts thus pointing to the same 
conclusion,—the greater elevation of the sea in the later 
part of the glacial period, while our present boulder-clays 
were being formed in the interior of the land, and deposited 
along the shores and in the neighbouring shallows of the 
glacial ocean.— Translator. | 
Where this marl is absent, the reason will be found to 
be the absence from the neighbourhood of such Silurian 
rocks as alone supply the materials from which it is formed. 
As has been already mentioned, the marl sometimes inter- 
changes endlessly with thinner or thicker layers of glacial 
sand, and wherever it does not rest directly on the scratched 
rock below, it is only separated by glacial sand or debris. 
In general, no shells are found in the marly clay, the ice- 
cold fresh glacier water from which it was deposited being 
unfavourable to molluscan life, which would only develop 
itself in the salt water of the greater depths, or where at 
least the fresh water was largely mingled with the sea.— 
[These localities are still probably hidden from us below 
the present sea-level. We have, perhaps, instances of them 
in the Elie bank (p. 27), and the Drobak bank (p. 25).— 
Translator. | 
NEW SERIES. —VOL. XVIII, NO. 1.—JULY 1868. B 
