NOVEMBEB 1, 1892.] 



KNOWLEDGE. 



203 



south-westerly direction down a fold of the hills which 

 crosses from the glaciers in question to the glacier 

 de Bionnassay ; when it reached the side of this glacier it 

 impinged on the lateral moraine, but was driven back by 

 this against an older moraine which it scooped out into a 

 great cirque. These moraines yielded to the impetus of 

 the moving mass of water and ice. and joined in the 

 mad race which the rushing mass now pursued down 

 the valley between the older lateral moraine and the 

 present lateral moraine, until it reached the bottom of the 

 Bionnassay glacier, near which it joined the stream from 

 that glacier, and thenceforward travelled in its course, 

 overturning first a chalet in the wood, where were an old 

 woman and some cows : then leaving the village of 

 Bionnassay safe on its height above the stream it passed 

 downward to Bionnay, which it almost entirely destroyed, 

 joined the course of the Bon Nant and rose as the gorge 

 narrowed to a great height, from which it fell with 

 remorseless energy on the doomed baths of St. Gervais. 

 Thence it continued its course through the beautiful 

 grounds of the establishment till it reached the junction 

 of the Bon Xant and the Arve, at Le Fayet, where it spread 

 out into a horrid flood, that is now represented by a great 

 expanse of grey mud and sand and wreckage, extending 

 far and wide over what was before a populous and fertile 

 stretch of country. 



The course of the avalanche as above described is traced 

 on the second sketch map by arrows which indicate its 

 direction. It may in like manner be traced on Figs. 8 and 9. 

 Fig. 8 is a general view of this part of the mountain range 



-.-^^---^ 





Fig. 9. 



-V Aiguille du Gouter. vv Aiguille de Bionnassay. v vv Glacier de 

 Bioonassav. The arrows indicate the coui"se of the torrent. 



taken from Prarion, north-west of the glacier des Tetes 

 Eousses ; and Fig. 9 is a key to Fig. 8, indicating the 

 course of the torrent by arrows. 



Some notion of the momentum of the moving mass of ice. 

 mud, and water maj- be gained not only from the destruc- 

 tion of the buildings at the baths of St. Gervais, liut fi-om 

 the movement of great stones, or rather rocks, which it 

 effected. One in particular, of vast dimensions, is shown on 

 the right hand of Fig. 10. The villagers of Bionnay were 

 intending to celebrate a/eVc on the 14th July, and witji a 

 view to letting off Uu.r </»> joif on that occasion holes had been 

 bored in a stone then in the village. That stone, with its 

 holes, is now at St. Gervais, and was probably highly effective 

 in the destruction of the baths. It is rather a rock than a 

 stone. It is further stated that the iron safe in the office 

 of the baths was can-ied five miles down the stream to 

 Sallanches, where it was foimd {Timeti, 15th .July, 1892). 

 These facts are of great interest, as the power of water to 

 move great masses of stone for long distances has been 

 a moot point amongst geologists and students of glat^ers. 



This explanation leaves many things tmexpaiued. 

 Under what circumstances will water accumulate as 'water 

 in the body of a glacier "? What, in this particular case, 

 caused the two great cavities and the communicating 

 passage ? Were they formed by some blocking tip of 

 "moulhis," or "glacier wells," as suggested by Mr. -Justice 

 Wills in his letter to the Times (16th July, 1892), or 

 •• originally caused by sub-glacial collapse'" as suggested 

 by Mr. Von Lindenfeld in Xatiin' (1.3th September, 1892) ? 

 'See also the letter of M. Delebecque in Xatuir of the 22nd 

 September, 1892.] How did the falling roof 

 of the upper hole acquire sufficient momentum 

 to do all the work that it did ? Was its weight 

 augmented by some mass of snow or ice that 

 fell suddenly upon it fi'om above ? Was the 

 water in the ca%-ities adequate to carry down 

 the vast mass of matter which descended ? or 

 was it increased from water stored in crevasses 

 which have disappeared with the fall of the 

 glacier ? or was ice reduced into water by fric- 

 tion in the downward rush of the mass (as 

 Prof. Forel would have us believe) "? Was the 

 impact of the water the sole cause of the de- 

 tachment of the glacial mass, or was there some 

 rent in the glacier existing before the water 

 operated which predisposed the glacier to break 

 up under any blow which it might receive "? 

 Was the draught produced by the sudden slip 

 of the glacier sufficient to evacuate the two 

 holes of their fluid contents, or was there some 

 other co-operating cause ? Lastly, is the account 

 above given in error in suggesting that the roof 

 of the upper ca%'ity was the first thing to move ') 

 or was it, on the contrary, the glacier on the 

 slope which gave the initial motion, and did 

 the roof of the upper cavity only yield to the 

 suction produced by the sliding ice ? These 

 can ask, but I cannot answer, 

 suggested that it is probable that the 

 was due to two causes — the one, an 

 ion of snow and ice, so great as to 

 fracture on the slope, and the other, 

 the action of the water on this unstable mass. 



As regards the first of these causes, the facts 

 in reference to the glaciers of Mont Blanc are 

 in favour of it. It is well known that for some 

 years past these glaciers have been on the in- 

 crease, that the balance of deposition and waste 

 is now in favour of deposition, and not as it was 



