VERTICAL DISTRIBUTION OF BRITISH LEPIDOPTERA. 5 



north, or above that, of the preceding zone. To it accordingly 

 belongs the great bulk of our indigenous Lepidoptera. In the 

 South of England this zone extends to the height of about 1800 

 feet above the sea-level ; but in the North of Scotland it sinks to 

 as low as 300 feet. No very familiar or typical botanical pro- 

 ductions may be enumerated as belonging exclusively to the 

 Lower Hill zone in this country. 



3. The Upper Hill zone is the British equivalent for Speyers' 

 2nd or Hill zone, also of Watson's super-agrarian zone, and 

 terminates at the isotherm of 41° F. It constitutes the highest 

 (or most northern) limit to which grain can be cultivated, and it 

 is likewise the point at which the oak and the common bracken 

 {Pteris aquiliiia) cease to grow. In the Grampian mountains it 

 terminates at the height of 1800 feet above the sea-level, but in 

 the Snowdonian range of North Wales it is somewhat 1000 feet 

 higher. By reason of its greatly reduced extent in this country, 

 this zone only contains a small proportion of the species of Lepi- 

 doptera found in the preceding zone. Erebia epiphron (var. 

 cassiope) is the sole species of butterfly which exclusively inhabits 

 this zone, and it is the only true alpine species of Ehopalocera 

 which we possess in the British Isles. It does not, however, here 

 ascend, comparatively, to anything like the height that it does in 

 the mountains of Central Europe, where it exists in Speyers' pine 

 or Lower Alpine belt, 



4. Tlie Loiver Alpine zone corresponds to the zone of the 

 same name defined by Messrs. Speyer, but from its very circum- 

 scribed extent it only possesses comparatively a small number of 

 species of Lepidoptera, although several species of butterflies are 

 known to breed within its boundaries. In England and Wales it 

 only contains a few mountain summits within its limits from the 

 height upwards of about 3000 feet, but in Scotland it constitutes 

 a much more extensive area in the Grampians, where it rises to 

 the height of about 3300 feet, terminating at the annual isotherm 

 of 36° F. This zone constitutes the highest limit to which the 

 heaths will grow, Callima vulgaris being the last species to 

 succumb to the increasing cold. In Switzerland, Germany, and 

 Scandinavia, it is the highest altitude at which the various 

 species of pine will survive, but the Scotch fir {Finns sylvestris), 

 which only grows to the height of 2100 on the Grampians (and 

 therefore only just enters the present belt), is of no value in 

 estimating the British equivalent for the zone in question, as this 

 tree is known not to reach to nearly so great an altitude as several 

 other species of the Coniferte, to which it belongs. I have, there- 

 fere, been compelled to adopt the common heath as the typical 

 plant of this belt or region. 



5. TJic Upper Alpine zone is of still more limited extent than 

 the preceding one, containing only the summits of the highest of 

 the Grampian mountains (from about 3300 feet above the sea- 



