250 ACTION OF FORESTS ON THE FLOW OP EWEBS. 



the Grandes-Communes, taking a deviation to the north of Digne. It 

 is against this chain that the first great storms of rain dash them- 

 ■ selves. The clouds in passing over these mountains seek the cols or 

 lower parts, and they arrive in the valley of the Ubaye by the openings 

 of Grande-Commune, of Enohastrayes, of the Cold' Alios, of theLawerq, 

 of the Bas, and in fine, by the great passage of the mountains of the 

 Seyne. 



" The fmhn forces a passage for itself into the valley of the 

 Durance ; goes up this throughout its whole length ; it makes its way 

 also by some cols of the chains which separate this valley from that 

 of the Ubaye, and more especially by those which are opposite Embrun. 



" If now the forest chart of the country spoken of and the chart of 

 the/osAwbe compared, it will be seen that the mountains of Seyne 

 have been cleared of woods, and that the whole southern upper slope 

 of the. valley of the Ubaye is devoid of forests ; in a word, that all 

 the parts which bear the direct attacks of the foehn, — those which 

 arrest it — force it to ascend them, aud to pour upon them masses of 

 water, are all of them almost entirely cleared of woods. Here we 

 have no longer, as is the case above Mentou, a tropical sun to warm 

 the soil ; the wind has cooled down as it rose higher from the sea, 

 and it is obliged with fatal effect to precipitate in the form of rain the 

 moisture it has borne thither ; and at that place where the forests 

 are an absolute necessity, and where the most considerable quantities 

 of water fall, there it is that they have completely disappeared. 



" This summary is incomplete, but it may suffice to render intelli- 

 gible the general course of the orages, or storms of rain in the Alps, 

 and the ii;itensity of these on certain parts, which are generally those 

 at which the foehn is compelled to rise considerably or to change its 

 direction. The celebrated torrent of Riou-Bordoux, near Barcelonette, 

 in face of the opening at Alios, is exactly so situated. The portion of 

 the Alps situated below the department of the Isfere almost completely 

 relieves the fcehn of its humidity, and this is the classic region of the 

 orages. 



" The fcehn does not confine itself to the production of torrential 

 rains ; it is not less terrible in its action on the snow, and on the 

 glaciers. As has been stated, it blows sluggishly and warm for one, 

 two, or three days before the rain appears ; if at this time the ground 

 be covered with snow this is not slow to melt rapidly, and absorbing 

 a great quantity of water it becomes like a sponge ; then supervenes 

 the rain which expedites the process and brings on a kind of debdcle, 

 or breaking up, and the water arrives in great quantities in the 



