By the end of
the Tertiary Britain had moved north to about its present latitude.
It was during the Quaternary that a general lowering of world
temperature took place which heralded the beginning of a series of
very cold to temperate periods collectively known as an Ice Age. 
During
these last 2 million years ice sheets have repeatedly advanced over
large areas of North America and Northern Europe on at least four
occasions. Various estimates of the thickness of these ice sheets
have been made, some being up to one kilometre thick.
Between glaciations the climate improved resulting in interglacial periods. Our present climate is more than likely an interglacial one. Glaciations, especially the last one which ended about 10,000 years ago, had a profound influence on the landscape as we see it today. During the last glaciation, known as the Devensian, Highland areas, such as the Lake District, Scottish Highlands, Southern Uplands and the Cheviot Hills generated ice caps from which ice sheets and glaciers travelled eroding huge amounts of material on their way. Hollows, known as corries in mountain sides and U shaped valleys were produced by the erosive power of ice. This material was redeposited across much of the lowlands as far south as the Midlands. Most of Northern England up to about 1000ft. has a covering of boulder clay. The effects of the last glaciation are not yet over; Scotland is still rising as it recovers from the weight of ice, while much of England is sinking.
Glacial erosion.
At present
about 10% of the earth's surface is covered by ice. Ice forms on land
when the temperature is low enough for snow to exist all year round.
As the snow layers build up the lower levels solidify into ice. The
ice will then begin to move due to gravity and a glacier develops.
When glacier
ice moves over a land surface it erodes by plucking, gouging and
grinding. Plucking occurs when pieces of bedrock frozen in the base
of the ice and are plucked out when the glacier moves. Debris
collected by plucking provides the tools for grinding and gouging the
rocks beneath. Gouging by larger fragments can produce grooves in the
underlying bedrock. These grooves are known as glacial striations.
Some material may be carried on the surface of a glacier, usually
frost shattered debris that has fallen onto the ice from higher ground.
It is the
enormous erosive power of glaciers that have produced the
characteristic landscape seen in the Lake District, such as the U
shaped valleys and the corries and tarns at the heads of the valleys
where the ice accumulated. When two glaciated valleys are adjacent to
each other, a narrow steep sided ridge is produced known as an
arête, a classic example being Striding Edge in the Lake
District. Many glacial valleys have been flooded by lakes, e.g. Thirlmere.
Meltwater from
glaciers and ice sheets can also cut erosive channels. These can be
marginal to an ice sheet or a channel created by an overflow from an
ice dammed lake. These channels produced by meltwater are known
collectively as glacial drainage channels or spillways. Classic
examples are Newtondale Gorge which runs north-south from near
Goathland to Pickering and that of the Forge valley near Scarborough.
