Chiefly Geological 153 



circumstances alter cases in other spheres besides our own. 

 Here, again, the spore of a fragile-looking fern, or the seed 

 of a whortleberry, may have fallen into a chink, and found 

 nourishment enough to sustain it. Of moisture there is 

 generally no lack, where mist hangs heavily over the 

 mountain so many hours of the week, and where copious 

 rain often descends without its presence being suspected in 

 the valley below. The plant takes root, and lives there ; 

 but the situation is too shelterless for it to dare to send up 

 a leaf over an inch or two in height ; and to flower is, for the 

 present, quite out of the question. Its only resource is in 

 patience. By slow degrees the roots push their way down- 

 wards and on every side, perhaps even enlarging the crack 

 as they grow ; and little by little the soil accumulates round 

 them, more from the decay of the plant's own scanty 

 vegetation than from anything else. But sparse though 

 that vegetation may be, the leaves are continually collecting 

 small quantities of carbonic acid from the atmosphere, which, 

 with the humus acids arising from their own decay, are 

 slowly but surely eating away the hard rock, and filling the 

 cranny with more nourishing plant food. As more and 

 more alkaline matter is dissolved from the rock, the soil in 

 the cranny becomes more and more potent as a rock- 

 destroyer, and as a plant-fertiliser, till at length, perhaps, 

 the crack extends right through the stone, and one day the 

 lower portion falls with a crash, leaving somewhere in its 

 fall a scant accumulation of soil, to go on repeating the 

 same process of disintegration elsewhere. Our plant may 

 perish in the ruin it has been so largely instrumental in 

 bringing about, perhaps even before it has opened a single 

 flower, or borne a single seed, though it may be as old as 

 the largest oak in the valley below. But, on the other 

 hand, it may find another lodgment in its fall, or the 

 original rock may not be so easily cracked ; and for years 

 before the catastrophe takes place, the plant may have so 

 enlarged its little hoard of soil that it has tempted other 

 neighbours to lend a hand in the work of colonisation. In 

 a situation near a mountain top, probably one of the next 

 seeds to find lodgment in the cranny may be that of a 



