Britain: The physical background

« Northern Ireland is 8° 10' West.

It is just under 600 miles (966 km.) in a straight fine from the south coast to the extreme north of mainland Britai n and about 300 miles (483 km.) across in the widest part.

Owing to the numerous bays and inl ets no point in Britain is as much as 75 miles (121 km.) from tidal water.

The seas surrounding the British Isles are everywhe re shallow — usually shallow waters are important because they provide excellent fishing grounds as well as breeding grounds for fish.

The North Atlantic Current, the d rift of warm water which reaches the islands from across the Atlantic, spreads out over the shelf and its ameliorating effect on the air is thus magnified.

The effect of tidal movement is also increased by the shallowness of the water.

II. Geology and Topography Despite their small area, the British Isles contain rocks of all the main geological periods.

In Great Britain the newer rocks, which ar e less resistant to weather and have thus been worn down to form low land, lie to the south a nd east, and the island can therefore be divided roughly into two main regions, lowland Brit ain and highland Britain.

In lowland Britain the newer and softer rocks of so uthern and eastern England have been eroded into a rich plain, more often rolling t han flat and rising to chalk and limestone hilly, but hardly ever reaching a thousand feet (30 5 meters) above sea level.

Its boundaries run roughly from the mouth of the Tyne in the north-eas t to the mouth of the Exe in the south- west.

Highland Britain comprises the whole of Scotland (i ncluding the hilly and moors of southern Scotland as well as the mountains of the S cottish Highlands, which extend from the Forth-Clyde valley to the extreme north-west), the Lake District in north-west England, the broad central upland known as the Pennines, almost the whole of Wales, and the south- western peninsula of England coinciding approximate ly with the counties of Devon and Cornwall.

Highland Britain contains all the mountai nous parts of Great Britain and extensive uplands lying above one thousand feet (305 meters).

This high ground, however, is not continuous but is interspersed with valleys and pla ins.

Geologically the mountains and hills consist mainly of outcrops of very old rocks (archa ean and palaeozoic), while the upper strata in the valleys and plains are mainly more recent (c arboniferous age) and similar to those in the northern and western parts of lowland Britain.

These carboniferous strata are rich in minerals and include the coal measures which were the foundation of Britain's industrial expansi on.

The outcrops and shallow seams of coal which have now largely been exhausted were found on the edge of the plains and up the valleys leading to the high land.

Most of the prese nt deep coal workings underlie the fertile lowlands.

Towards the end of Britain's long geological histor y, when the ancestors of present- day man had already settled in the country, came th e great Ice Age during which, at one period or another, ice caps and ice sheets extended approximately as far south as the Bristol Channel and the Thames valley.

The ice naturally ac cumulated on the higher ground and swept from the mountains of Scotland, northern Engl and and Wales any loose rock or soil which had previously been formed, so that, when the ice eventually disappeared, the hills stood out as barren rocky areas, while a thick mant le of glacial debris—boulders, boulder- clay, sands and gravels—lay distributed widely over the lower ground.

The ice had blocked up previous drainage channels and left large lakes, which have since gradually dried up, leaving deposits of sand, silt and mud, often affor ding soils of great fertility.. »