
896 STRATIGRAPHICAL GEOLOGY. [Book VI. 
In the later stages of the Glacial Period the records are much the 
same all over Britain, allowance being made for the greater coldand 
longer lingering of the glaciers in the north than in ” the south, and 
among the hills than on the plains. 
In Scotland the following may be taken as the average succession of 
glacial phenomena in descending order : 
Last traces of glaciers, small moraines at the foot of corries among the higher 
mountain groups. 
Marine terraces (50 feet and higher). Clay-beds of the Arctic sea-bottom 
(Clyde beds) containing northern molluscs. 
Large moraines coming ‘down even to the 50-feet raised beach, showing that 
the glaciers of the second period descended to the sea-level in some places. 
Erratic blocks. These were partly transported by the first ice-sheet, partly 
by the later glaciers, and partly by floating ice during the period of sub- 
mergence. 
Sands and gravels—Kame or Esker series, sometimes containing terrestrial 
organisms, sometimes marine shells. 
Upper boulder-clays—rudely stratified clays with sands and gravels. 
Till or lower boulder-clay (bottom moraine of the ice-sheet)—a stiff stony 
unstratified clay, varying up to 100 feet or more in thickness. It contains 
intercalated bands of fine sand, finely laminated clays, layers of peat and 
terrestrial vegetation, and bones of mammoth and reindeer (nter-glacial 
beds), also in some places fragments of Arctic and boreal marine shells, in 
other places less fragmentary assemblages of similar shells, which prove a 
submergence of at least 524 feet below the present level of the sea. The 
boulder-clay spreads over the lower grounds, often taking the form of 
parallel ridges or drums. 
Ice-worn rock surfaces. 
Over a great part of England and Ireland the drift deposits are 
capable of subdivision, as follows: 
Moraines and raised beaches. 
Upper boulder-clay—a stiff stony clay with ice-worn stones and intercala- 
tions of sand, gravel, or silt. It has a more sandy and less unstratified 
aspect than the lower boulder-clay, and occasionally contains marine 
shells. 
Middle sands and gravels, containing marine shells. At Macclesfield 200 
feet above the sea) the species include Cytherea chione, Cardium rus- 
ticum, Arca lactea, Tellina balthica, Cyprina islandica, Astarte arctica, 
and other shells now living in the seas around Britain, but indicating 
perhaps by their grouping a rather colder climate than the present. At 
Moel Tryfaen near Caermarthen a similar assemblage of shells has been 
met with at 1350 feet above the sea. Near Yarmouth the middle glacial 
beds have yielded shells of a more southern aspect. In Ireland also the 
middle sands and gravels have furnished marine shells of living British 
species at heights of 1300 feet above the sea. 
1. Lower boulder-clay—a stiff clayey deposit stuck full of ice-worn blocks, 
and equivalent to the till of Scotland. On the east coast of England 
it contains fragments of Scandinavian rocks. Along the Norfolk cliffs 
it presents stratified intercalations with bands of gravel and sand, which 
haye been extraordinarily contorted. As in Scotland the true lower 
boulder-clay in the north of England and Ireland is often arranged in 
parallel ridges or drums in the prevalent line of ice-movement. As 
above mentioned the so-called “crag” of Bridlington, Yorkshire, is 
probably a fragment of an old marine glacial shell-bearing clay, which 
has been torn up and imbedded in the boulder-clay of the first ice-sheet. 
oo 
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Scandinavia.—The order of Pleistocene phenomena is generally the 
same here as in Britain. The surface of the country has been every- 
where intensely glaciated, and the ice-strie show that the great ice-sheet 
