310 THE REVOLUTIONS OF THE CRUST OF THE EARTH. 



dissolvant, pass into the crystalline state, and in this condition always 

 contain what is called the water of crystallization. If the materials are 

 not soluble, they form sedimentary beds, which retain the water in 

 which they were deposited. Whoever has visited the quarries of hewn 

 stone, and especially those of calcareous rocks, will be convinced of this 

 fact ; the freshly raised stones are soft and much easier to cut, as they 

 have not lost their quarry-water. The aerolites also contribute to the 

 absorption of water ; the substances which constitute them, being inoxi- 

 dized, absorb oxygen, and are afterward hydrated, forming deposits 

 similar to those produced by bodies of terrestrial origin. 



If the fluid envelope constantly diminishes, its action decreases in 

 proportion, but with such extreme slowness that even after the lapse of 

 several centuries there would be no apparent change in its condition. 

 In the present state of our globe, we inay say that nothing resists the 

 slow and continued action of atmospheric forces. Everything is cor- 

 roded and destroyed in the course of time by these powerful agents. It 

 is their slow action which has hewn and fashioned the rocks of Swiss 

 Saxony, whose singular forms and bold superpositions astonish the trav- 

 eler. It is through their influence that the mountains are cleft with 

 deep ravines, that the plains are furrowed by streams and rivers, which 

 act as so many veins in this gigantic circulation where all proceeds from 

 the sea and all returns to the sea. 



The vapors which arise from the ocean through the influence of solar 

 heat are, above the continents, condensed into rain, which, falling upon 

 slopes of variable inclination, carries away in the streams formed all 

 debris which, on account of the impulse of the waters, size or form, can- 

 not resist the action of the water. When this debris reaches the rivers, it 

 is there deposited in proportion as the rapidity of the waters diminishes, 

 and fills up the beds of the rivers, which, in consequence, often change 

 their course. Several rivers of Upper Italy, and especially the Po, have 

 filled up their beds to such an extent that, in order to avoid the frequent 

 floods which occur whenever the rivers are at their full height, it has 

 been found necessary to raise the banks by means of dikes, an immense 

 and almost interminable undertaking. Agriculture has^ however, de- 

 rived great advantages from this circumstance ; for, as the water is 

 higher than the surrounding country, it can easily be directed to all 

 points where, for agricultural or other needs, it is required in great quan- 

 tity. Fields of rice are thus inundated, gardens and fields supplied with 

 moisture; in fact water is the nerve of the industrial and agricultural 

 life of Lombardy, of Venice, and of the neighboring countries on the 

 right shore of the Po; it is the source of the prosperity of the regions. 



Toward the mouth of the rivers are deposited the finer materials, which 

 have been retained in suspension in the water, and these form the sand- 

 deposits which extend more and more into the sea, that is if the latter 

 is tranquil, and if the action of the tides and waves is not too great ; in 

 the contrary case, these deposits, which are called deltas, on account 



