146 



HARDWICKE'S SCIENCE-GOSSIP. 



deposit which forms the capping of all of the hills 

 in Gozo and Malta, it had, in bygone years, taken 

 root, and disseminated a perfect network of tough 

 fibrous tendrils throughout every available nook and 

 cranny. 



In the mean time, the subjacent sand beds had 

 been slowly eroded away by those atmospheric 

 agencies that were constantly assailing them, and 

 thus the upper limestone masses, deprived of their 

 foundations, were left in a state of unstable equi- 

 librium, which rendered them susceptible of the 

 least mechanical strain, whether exerted from above 

 or below. 



The end soon came. Many of the rootlets had 

 decayed, and becoming intermixed with other 

 vegetable matter that had entered the fissure with 

 the rain, a humus had formed, from which carbonic 

 acid gas was evolved ; this, acting on the limestone, 

 caused an enlargement of the fissure, and the mass 

 of rock thus attacked and weakened in every direction, 

 at length broke off from the parent bed, and 

 thundered down the slopes to the bottom of the 

 valley. The tree was reft in twain by the force of 

 the separation ; and now gaunt and bare, its mutilated 

 trunk sways to and fro with every breeze, as though 

 moaning over the fate that had deprived it of its erst- 

 while home. 



" Cast anchor in the rifted rock, 

 And o'er the giddy chasm flung 

 His shattered trunk, and frequent flung, 

 Where seemed the cliffs to meet on high, 

 His bows athwart the narrowed sky." 



Among the multiplicity of causes at work, 

 hollowing and scooping out the caves that occur 

 so plentifully all along the escarped sides of the 

 valley, none are more indefatigable in their exertions 

 to forward the work of destruction than the innocent- 

 looking, sweet-smelling mint (Melissa officinalis), and 

 the delicately-formed maiden-hair ferns, with which 

 the walls and floors of the caverns are often draped. 

 Carefully remove two or three of these plants from 

 their places, and note how they have converted the 

 upper film of the rock itself into a soil wherewith to 

 assist them in their struggle for existence. Yonder 

 wall, with its rich green mantle of ivy, deserves, too, 

 a share of attention. How the tendrils of this hardy 

 little creeper have inserted themselves into the most 

 impossible of places, and have threaded and re- 

 threaded the interstices until they have bound the 

 whole mass as no mortar could have done it ; but let 

 us lift this grey green garb and expose the rottenness 

 that exists beneath. The stones appear to be in a 

 rapid state of decay, owing to the humid nature of 

 its surroundings, a state which is clearly attributable 

 to the plant-life that covers it, for see, those very 

 parts that are not so covered, have successfully 

 withstood all the combined attacks of the 

 atmospheric forces to which it had constantly been 

 subjected. 



But of all of the plants that contribute towards this 

 wasting away of the island deposits, the cactus or 

 prickly-pear stands pre-eminently the first, as being 

 the one to which the most mischief is due. 



This plant is extremely hardy, and grows in great 

 abundance, anywhere and everywhere in the islands. 

 No soil seems to be too poor for it to take root in, 

 and as soon as one of its oval, fleshy leaves is set, in 

 the course of a comparatively short time a small 

 forest of them may be anticipated. It often attains a 

 considerable size, ranging from one to fifteen feet in 

 height, and the fruit, which is of a rich red and 

 yellow colour, is used by the peasantry as food, both for 

 themselves and for their cattle. Like all other trees 

 of vigorous growth, it does not confine itself to 

 the soil, but causes its roots to ramify in all 

 directions, and wherever it is possible to penetrate 

 the underlying strata in search of those phosphates 

 and carbonates that are necessary to its existence, and 

 in which the soil may be deficient. 



But the work of breaking up the rocks and con- 

 verting them into soil represents only a very small pro- 

 portion of the actual part which it plays as an agen 

 of degradation. 



The humus, formed by its decaying portions, 

 evolves large quantities of carbonic acid gas, or 

 carbonic dioxide, and this, when dissolved in water, 

 imparts to the water some peculiarly destructive 

 properties. 



Pure rain-water, when alone, has but little effect 

 upon lime ; but, in conjunction with this gas, its 

 dissolving powers aie increased fifty-fold. 



The rain-water that descends upon this decaying 

 mass of vegetable matter, saturates itself with the 

 carbonic dioxide, and then percolates through the 

 limestone, and dissolves and carries away in solution 

 the carbonate of lime of which it is largely composed. 

 Evaporation follows, and by means of another 

 chemical change this lime is again deposited as an 

 insoluble substance, known to chemists as bi-carbo- 

 nate of lime. 



In this way vast caverns are formed in the very 

 bowels of the earth, and many of them are found 

 draped and festooned in a most fantastic manner, 

 with stalactites and stalagmites that have been de- 

 posited after the evaporation of the water, which has 

 done the work of excavation. 



The "Ta Ninu " cavern on the " Ta Xaghra" 

 hill at Gozo, and the stalagmitic cavern, popularly 

 known as "Calypso's Grotto," in which the love- 

 stricken goddess is said to have held her court, and 

 to have entertained Telemachus after his shipwreck, 

 may be cited as examples of the magnitude of the 

 work effected through the instrumentality of objects 

 apparently so trivial and insignificant. 



But let us descend the terraced sides of the valley, 

 passing en route the gnarled and twisted trunks of 

 numerous carob trees, pomegranates, German 

 medlars, wild plum trees, orange trees, silken-rye 



