HARDWICKE'S SCIENCE-GOSSIP. 



J 45 



TREES AND PLANTS AS AGENTS OF DENUDATION. 



By JOHN H. COOKE, B.Sc, F.R.G.S. 



FTEN when ramb- 

 ling through the 

 rocky gorges and 

 beneath the craggy 

 escarpments of 

 these islands, my 

 attention has been 

 drawn to the silent 

 though effective 

 manner in which 

 the humblest 

 agents in the 

 economy of nature 

 have their energies 

 directed and hus- 

 banded, in order 

 that the greatest 

 effect may be pro- 

 duced with the 

 least expenditure 

 of energy. How 

 many would imagine that the same plant life 

 which clothes the mountains, valleys, and plains on 

 the earth's surface, and which imparts such a charm 

 to what would otherwise be all that is sterile and 

 desolate, is one of the most unremitting of the many 

 agencies that are at work in degrading down the 

 rocks of which the earth's crust is composed ? 



Year after year they play their part, unobtrusively 

 it is true, but so sure and certain that as ages elapse 

 the most stupendous changes are wrought in the 

 contour of the earth's surface. 



Measured by human experience, the changes are 

 slow, and are but of little importance. The short 

 span of existence allotted to man is not sufficient to 

 allow him to appreciate their full significance, unless 

 he is prepared to look back into the past and, using 

 his own experience as an index, to consider the 

 aggregated changes that have been effected through 

 the instrumentality of apparently such insignificant 

 causes. By so doing, he may arrive at not only an 

 No. 307. — July 1890. 



approximation of the condition of things that formerly 

 existed, but may also obtain some idea of the 

 nature of those forces that are constantly engaged 

 in the work of destruction. 



There is no spot in the two islands that will afford 

 more genuine pleasure to the lover of Nature than 

 will the charmingly situated valley of Emtahleb, with 

 its rippling, purling streams and verdure-covered 

 slopes ; and that will, at the same time, afford more 

 excellent opportunities for examining closely the 

 conditions under which the plant life of the caves 

 and gorges exists, and the part it plays both in 

 protecting and destroying the rock surfaces upon 

 which it grows. 



Innumerable opportunities will present themselves 

 to enable one to observe the shifts to which the 

 larger trees resort in their struggle for existence. 

 The rich though scanty soil that covers the slopes 

 is not of sufficient depth to enable them to obtain 

 that hold in it that their great size demands, and 

 they therefore insert their roots into the cracks and 

 crevices of the sandstone; and then, as in course ofi.time, 

 the increased bulk of the underground branches 

 necessitates more space than the confined limits of 

 the place will allow, the rock is shattered into- 

 fragments as effectively as though it had been 

 subjected to the blows of a Brobdingnagian hammer. 



Descending the tortuous path which leads to the 

 springs at the bottom of the valley, an excellent 

 example of the manner in which even a single tree 

 may alter the physical aspect of the country in its 

 immediate vicinity, is to be seen on the top of the 

 cliffs that fringe its northern side. 



The gaunt, spectral trunk of an old carob tree 

 overhangs the beetling brows of the rugged limestone 

 cliffs, and seems to invite inquiry into the manner in 

 which it has obtained its strange position. It tells 

 its own tale readily enough, and almost seems to be 

 proud of the work of destruction in which it has 

 been concerned, and which ultimately brought about 

 its own ruin. In a fissure of the upper limestone, a 



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