mTRODUCTION. 



13 



on some lands, on whioli the remedy wonld not be inappropriate, may be 

 considered a satisfactory reason for delay, I may state that I admit without 

 hesitation that to produce such torrential flows as has been seen in the 

 Alps the quantity of rain falling there must be very great ; but I must 

 add that the effect of the rainfall on water-courses depends more on its dis- 

 tribution over time and space than on its average annual amount, and that 

 oroffes, or storms of rain, constitute one of the peculiar meteorological 

 phenomena of the High Alps. M. L. Marohand, Garde General dis Forks, 

 says on this subject, — " When the torrential rains of the Alps are made a 

 subject of study it is soon seen that they are aU of them occasioned by a 

 particular wind called the fahn. These winds are generally violent, and 

 present almost always the character of orages, or storms of rams ; it follows 

 that great quantities of rain are .poured down upon the soil ; abd to this 

 may be attributed disasters sometimes coming upon spots which seemed to 

 be placed in the best possible situation and circumstances to bear the most 

 persistent rains. 



" The fcehn is a wind which blows from the south, often with extraordinary 

 force ; it is peculiar to the Alps, and is felt throughout their whole extent. 

 Having climbed over Italy where it is no other than the droeo, the 

 following are its chief characteristics : — It comes from the south, but its 

 direction is modified at every step, either by moimtain chains or by valleys. 

 Its origin is still a subject of discussion : according to some it originates in 

 the Sahara, according to others it originates in the GuK of Mexico. It 

 gives to the sky a strangely-marked, peculiar, heavy, whitish aspect ; and 

 the rain falls on the second or third day following its appearance. 



" The wind arrives on the Mediterranean coast loaded with vapour ; it 

 there encounters that immense calcareous simi-circular wall of the Maritime 

 Alps, and it scales their higher slopes ; but in consequence of their covering 

 of forests, and the great heat concentrated by them, in doing so it only 

 attains a higher temperature. It is rarely the case that the moisture is 

 condensed or precipitated on these countries which it rapidly traverses ; but 

 it cools by degrees as it mounts the Maritime Alps, and on reaching the 

 upper basin of the Var and its affluents it deposits an enormous quantity 

 of water ; then it continues to advance northwards to French Comt6, before 

 reaching which latitude it has lost much of its force. 



" If a glance be cast over a map of the Southern Alps, it may be obsa^ed 

 that from Mount Vise there part off great chains running perceptibly from 

 east to west ; the fahn comes by the valleys of the basin of the Var, or of 

 the upper sources of the Durance, it strikes upon the first chain parting 

 from the col of the Pas-de-la-Cavale, or of the Grandes-Communes, taking 

 a deviation to the north of Digne. It is against this chain that the first 

 great storms of rain dash themselves. 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 Grange-Commune, of Enchastrayes, of the Col 

 d' Alios, of the Lawerq, of the Bas, and in fine, by the great passage of the 

 mountains of the Seyne. 



" The/ceAw 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 

 fcehn be compared, it will be seen that the mountains of Seyne have beea 



