PART I. 



BKSnME OF SUEELL'B STUDY OP THE TOEEENTS OF THE HIGH ALPS. 



Of numerous treatises on subjects connected with the natural history, and 

 the arrest or control of torrents in France, that by M. Surell appears to 

 have been that which has done most to give the direction to remedial 

 operations which has been pursued thus far with the happiest results. 

 There were writers before him who anticipated him in some of his sugges- 

 tions, and there are writers of the present day who have s^^ested more 

 advanced operations ; but that the work of SureU to which I have referred 

 had the effect I have indicated seems to be proclaimed by all. This wori, 

 entitled Etude sur les Torrents des Hantes-Alpes, was printed by order of the 

 Minister of Public Works, and published in Paris in 184:1. Theauthorliad 

 been engaged in engineering work on the High Alps, and his first intention 

 was to prepare a few notices of matters connected with engineering for 

 insertion in the Annales des Fonts et Ckaussees ; but becoming interested in 

 the subject, and being encouraged by the Prefect of the district, he was led 

 to make a study of water-courses and every thing connected with them. 



In the sequel I adhere not closely the order in which the several subjects 

 noticed are discussed by him ; but to some extent I follow that order, while 

 the division adopted is my own. 



Section I. — The PheTiomena of Torrents in the High Alps. 



M. Surell, to give precision to his treatise which relates to torrents alone, 

 classifies the water-courses of the High Alps as — ruisseaux, or mountaib 

 streams ; torrents ; rivieres torrentials, or torrential rivers ; and rivers : and 

 states what he reckons the distinguishing characteristics of these. He refers 

 also to glacier streams, and to what are known as torrents blanks, to point out 

 wherein they differ from what are known as torrents. 



In what are called torrents Manes the agency of water is scarcely perceived ; 

 it is in operation, but it occupies a very subordinate position ; in torrents it 

 is the one commanding power, acting with apparently resistless force. 



From the glaciers there proceed currents of water, and by them are 

 formed deposits of stones and rubbish, known as moraines, which might be 

 mistaken for beds of deposit formed by toiTcnts ; but these have character- 

 istics aU their own by which they may be easily destinguished from those. 



The ruisseaux, or mountain streams, are formed of a body of water, small 

 in comparison with the torrents of which he treats, and may form cascades 

 but not torrents, though they may become feeders of these. 



He describes the rivers of the High Alps, of which he enumerates four, as 

 flowing in wide valleys enolosed by elevated ranges of mountains or of bflls, 



