Pennine Hills, the Lake District mountain mass, and the Mendip Hills
were being most vigorously uplifted, while the granite masses of
Cornwall and Devon were perhaps being injected into the Carboniferous
and Devonian rocks. From this period, more or less of the Pennine
ridge has always remained above the sea, along with much of Cornwall
and parts of Devonshire.

In early Jurassic times the sea probably again occupied most of
England with the exception of the above-mentioned areas, the Lake
District and eastern part of the London Basin; Wales, too, and much of
Scotland were land. Elevation gradually caused more land to appear in
later Jurassic and early Cretaceous times when a river system, now
entirely obliterated, drained into the Purbeck estuary and Wealden
lake; but a subsequent depression led to the wide extension of the
Chalk sea. By the beginning of the Eocene period we find the sea
limited to the S.E. of England, where the London Clay, &c., were being
laid down. It was not until quite late in Tertiary time that these
islands began to assume anything like their present form. In the
earlier part of the Pleistocene period, England and Ireland were still
incompletely severed, and the combined activity of certain extinct
rivers and the sea had not yet cut through the land connexion with the
continent. The last well-marked lowering of the land took place in the
Pleistocene period, when it was accompanied by glacial conditions,
through which the greater part of northern England and the Midlands
was covered by ice; a state of things which led directly and
indirectly to the deposition of those extensive boulder clays, sands
and gravels which obscure so much of the older surface of the country
in all but the southern counties.

Throughout the whole period of its geological history, volcanic
activity has found expression with varying degrees of intensity along
what is now the western side of the island, with the exception that in
the Mesozoic era this activity was in abeyance. We may note the
pre-Cambrian lavas and tuffs of the Wrekin district in Shropshire and
the somewhat later volcanic rocks of Charnwood; the porphyrites,
andesites, tuffs and rhyolites of the Borrowdale volcanic centre,
erupted in the Ordovician period, and the Silurian granites of the
same region. The volcanic outbursts which followed became feebler in
the Devonian and Carbonife