The island of Ireland is situated in the extreme north-west of Europe between 511/2 and 551/2 north latitude and between 51/2 and 101/2 west longitude.The Irish Sea to the east, which separates Ireland from Britain, is from 17.6 to 192 km (11 to 120 miles) wide and has a maximum depth of about 200 metres (650 feet). Around the other coasts the shallow waters of the Continental Shelf are rather narrow and depths increase rapidly into the Atlantic Ocean.
The island comprises a large central lowland of limestone with a relief of hills surrounded by a discontinuous border of coastal mountains which vary greatly in geological structure. The mountain ridges of the south are composed of old red sandstone separated by limestone river valleys. Granite predominates in the mountains of Galway, Mayo and Donegal in the west and north-west and in Counties Down and Wicklow on the east coast, while a basalt plateau covers much of the north-east of the country. The central plain, which is broken in places by low hills, is extensively covered with glacial deposits of clay and sand. It has considerable areas of bog and numerous lakes.
The island has seen at least two general glaciations and everywhere ice-smoothed rock, mountain lakes, glacial valleys and deposits of glacial sand, gravel and clay mark the passage of the ice.Influenced by the Gulf Stream and with the prevailing winds predominantly from the south-west, the climate is equable and temperatures are fairly uniform over the whole country. The coldest months are January and February with mean daily air temperatures of between 4 C and 7 C, while July and August are the warmest (14 C to 16 C).
May and June are the sunniest months, averaging 5 to 7 hours of sunshine per day. In low-lying areas average annual rainfall is mostly between 800 and 1200mm (31" to 47") but ranges from less than 750mm (30") in some eastern areas to 1500mm (59") in parts of the west. In mountainous areas annual rainfall may exceed 2000mm (79").