20 Climate of the British Isles 



other peaks above 2000 ft.) ; several hills in the Pennine 

 range over 2000 feet ; and High Wilhays on Dartmoor 

 in Devon (2039 ft. = 621 m.). 



To the east of the imaginary line mentioned the 

 contrast is extremely striking. Palaeozoic rocks are not 

 represented at the surface, the gently undulating plains 

 are broken by comparatively few ranges of hills exceeding 

 500 feet (c. 150m.) in height; only the Cleveland massif 

 in north Yorkshire exceeds 1000 feet (c. 305 m.), and there 

 are no elevations reaching 1500 feet (c. 460 m.). 



Ireland, which is mainly composed of Palaeozoic rocks, 

 has its hilly regions in the north, west and south, enclosing 

 an extensive central plain of an elevation less than 500 feet. 

 The highest altitudes are found in Macgillicuddy's Reeks 

 (3414 ft. = 1040 m.) in the south-west, but there are several 

 other mountains exceeding 2000 feet (610 m.). 



The mild "oceanic" climate of the whole of the British 

 Islands is determined in the first place by 

 Causes of ^-j^g great length of coast-line compared with 



climate. ^^ total area, and the consequent general 



dampness of the air, which tends to lower 

 the temperature in summer and to raise it in winter. 

 This effect is of course a direct function of proximity 

 to the sea, as can be seen very strikingly by an examina- 

 tion of maps recording the mean maximum temperatures 

 for January and the mean minimum temperatures for 

 July. The lines indicating equal values are in both cases 

 concentric about the land masses'. 



The second great factor is the direction and character 

 of the prevailing winds. Owing to the nearly constant 

 position throughout the year of the north- Atlantic area of 

 low barometric pressure, in the neighbourhood of Iceland, 

 the prevalent winds during the whole year are from the 

 south-west, i.e. they are warm moisture-laden winds 

 coming from the warm regions of the mid- Atlantic and 



' Bartholomew's Physical Atlas, Part in. Meteorology , 1899, p. 11. 



