GENERAL 261 



Such forests only allowed settlements on the margins of 

 the valley meadows, and made even the barbarians pause 

 and go round. 



The areas of grass pastures, heather moors, and peat 

 bogs have been changed and generally extended and the 

 surface altered beyond recognition. Some portions have 

 been drained, others submerged, others again irrigated 

 or put beyond the reach of floods. Most* parts have 

 been cleared of timber, many given up to cattle and 

 sheep, many again burned yearly, whilst a large area has 

 been claimed by cultivation. Similarly the composition of 

 forests, bushes, and grasslands has been altered, by fire or 

 by grazing. A large extent of waste and derelict land 

 has been created, whose variable and heterogeneous plant 

 carpet, drawn from the adjacent formations, strives for 

 some kind of organization and balance. Numberless 

 species of plants have been imported by man, sometimes 

 competing successfully with the original denizens. Ulti- 

 mately, it is apparent that by altering the equilibrium of 

 the animal world, destroying many species and intro- 

 ducing others, the nature of the plant carpet has been 

 indirectly but powerfully affected. It is therefore diffi- 

 cult to do more than briefly to indicate the more obvious 

 correspondences between the vegetation and its regional 

 environment. 



In the middle of the deciduous belt various subalpine 

 heights form insulated areas of conifers. On the 

 Pyrenees, the Alps and the Carpathians, the coniferous 

 districts enclose cores of alpine vegetation. 



The Arctic Region. The most unfavourable conditions 

 offered to plant and animal life are found in the ice and 

 snow-fields of the arctic and alpine regions. An intense 

 frost and darkness during nearly a half of the year, 

 alternations of frostbound earth and icy water during the 



