HARDWICKE'S SCIENCE-GOSSIP. 



in planing down and moulding the hills and valleys 

 of the islands and shores of the Mediterranean, the 

 sirocco, a south-easterly wind that blows from the 

 dry, arid regions of Africa is, perhaps the most 

 remarkable. All of the districts situated within the 

 Mediterranean are affected, more or less, by it. Its 

 blighting influence on plant-life, and the depressing 

 and debilitating effect that it has upon the human 

 constitution, are but too well known to all .those 

 whose misfortune it may have been to have had to 

 spend the sultry days of a Mediterranean summer 

 within the sphere of its influence. Organic and 

 inorganic matter are equally affected by it, but while 

 the effect of its attacks on the former make them- 

 selves rapidly apparent, on the latter the processes 

 that it employs in its work are slow though effective, 

 and therefore the results to which they give rise are 

 proportionately retarded. This is even more apparent 

 in countries in the Mediterranean area which, like the 

 Maltese Islands, have a comparatively small rainfall ; 

 and where the catchment basins are restricted in size. 

 In such districts a large proportion of the denuda- 

 tion to which the surface contour of the district owes 



rounded masses are the dun-coloured marls, the 

 taluses of which often descend the slopes to distances 

 that are double, and even treble the real thickness of 

 the bed. These marl outcrops are a characteristic of 

 Maltese hill scenery. They owe their origin to the 

 percolation of water through the upper beds, whereby 

 the marl is rendered sodden, and then, being more 

 susceptible to the weight of the superincumbent rock 

 than when dry, it is pressed from out the strata, and 

 is precipitated down the hill-sides. 



The bases of the hills, therefore, have a cloak of 

 marl which effectually protects them from aerial waste, 

 while the upper portions, being without this protec- 

 tive influence, rapidly waste away before the humid 

 winds, and thus the slopes of the valleys are seldom 

 precipitous, and the isolated hills assume a distinctly 

 conical form. 



The hills and plateaux are thus shielded below by 

 their own ruins, while the wasting away of the upper 

 portions causes them to gradually assume the tapering 

 shape with which the student of Maltese scenery is so 

 familiar. 



Unlike the Globigerina Limestone, the Upper 



Fig. 2. — Gozo Hills, from the Sea. (N. side.) 



its diversified character, is to be attributed to the 

 slow and intermittent, though powerful, agency of 

 this wind. 



It is along the escarpments of the hills and valleys, 

 and in the cliff exposures that have a south-easterly 

 aspect, that its powers of erosion are to be studied to 

 the best advantage. 



The flat-topped conical hills that form such a 

 distinguishing feature in Malta and Gozitan scenery, 

 owe their origin, in a great measure, to its influence. 

 The Globigerina Limestone, the fourth bed from the 

 top, formation forms the base of all of these hills, and 

 on account of its homogeneity and softness of texture, 

 it readily disintegrates before the rapid alternations of 

 dryness and humidity that are the usual concomitants 

 of the Sirocco. 



This bed may be traced from the bottoms of all of 

 the valleys in the Binjemma and the Gozitan plateaux, 

 falling back in long-drawn swellings and gentle 

 undulations ; and covered with a rich and productive 

 soil, in which the crimson sulla (clover), and the 

 golden rye for which the islands are noted, grow 

 luxuriantly. 



Capping this bed, and still falling back in softly 



Coralline rock is not equally susceptible to the in- 

 fluences of this wind. But certain portions of the 

 strata, situated in the middle of the formation, 

 weather much faster than do the layers either above 

 it or below it. 



In the majority of cases this formation is found 

 capping the hills of both islands, and forming table- 

 lands, the sides of which are bounded by precipitous 

 cliffs that attain a height which is dependent upon 

 the local thickness of the formation. It also forms 

 the surface deposits of several undulating plains, and 

 it frequently occurs as shapelesss hummock-like 

 masses. These diversities of form are due in a 

 measure to the unequal waste that the rock undergoes, 

 as its mineralogical composition varies considerably, 

 some parts of the strata being so hard as to be 

 capable of withstanding the combined action of the 

 atmosphere for centuries, while other portious readily 

 disintegrate on exposure. 



It is to this unequal action that the formation owes 

 the craggy contour of its cliff outlines ; and it is this 

 that causes it to offer such marked contrasts to the 

 gentler undulations of the softer beds beneath. It 

 is from this formation, too, that the rock boulders 



