THE TUNDRA AND ITS ANIMAL LIFE. 69 



If the ground lies below the level of the surrounding plains, and 

 is therefore very moist, the bog-moss gains the day, and, gradually 

 crowding out the dwarf -birch, forms great swelling cushions. As 

 the root-parts rapidly die away into peat, these cushions become 

 higher and more extensive until the water impedes any further 

 advance, or else they break up into dome -like hillocks. If the 

 basin be very flat, the accumulated water rarely forms a lake or 

 pond, scarcely even a pool, but soaks through the soil to an indefinite 

 depth, and so forms a morass whose thin but tough covering of 

 interlacing sedge-roots can only be trodden in safety by the broad- 

 hoofed reindeer; and even his steps, and the deeply-sinking runners 

 of the sledge, make it yield and tremble like jelly. 



When the depression becomes a short confined trough, without 

 outlet, into which a streamlet flows, however slowly, the morass 

 becomes a bog, or lower down, a swamp. In the first of these, reeds, 

 in the second downy willows (sallows), a second characteristic 

 plant of the tundra, attain to luxuriant growth. Though only in 

 very favourable circumstances becoming as' tall as a man, these 

 plants form thickets which may be literally impenetrable. Their 

 branches and roots interlace to an even greater extent than do 

 those of the dwarf -firs on the mountains, forming an inextricable 

 maze which can best be compared to a felt compacted out of all the 

 diflerent parts of the willow. It withstands the strongest arm, 

 when one tries to clear a path through it, and it offers so much 

 obstruction to the foot that the most persistent explorer soon gives 

 up the attempt to pierce it, and turns aside, or retraces his steps. 

 This he does the more readily as the substratum is in most cases 

 morass or an almost continuous series of marshy, slimy pools whose 

 fathomableness one is unwilling even to try. 



As the traveller journeys through the tundra, he recognizes that 

 the whole region presents to the eye the individual features already 

 described, in regular alternation and monotonous repetition. Only 

 where a large river of considerable volume flows through the low 

 tundra is there any real change. Such a river deposits on its 

 banks the masses of sand it has carried down; and the wind, which 

 blows constantly and usually violently, piles these gradually up 



