60 2 



NA TURE 



[October i8, 1894 



developed in a plane perpendicular to the principal axis, 

 as flat snow crystals. When, however, the atmospheric 

 space is limited by a wall, first a small hexagonal disc of 

 ice attaches itself to that wall. Then, as growth pro- 

 ceeds, in a calm or comparatively calm medium, the 

 middle portion of the disc will be in contact with air 



Fig. 



\'I. Utcrature. — In 1697, Camerarius of Tubingen 

 (" De figura nivis et pruinas." Misc. ac. iiaiur. Jence, 

 Dec. 1697, p. 480) describes some hoar-frost on the lead 

 bindings of windows as hexagonal discs, some of which 

 had a central depression. 



Dr. I. Krenner mentions, in his description of the ice 

 cave of Dobschau ("A Dobsinai Jogbarlang.'' Budapest, 

 1S74), flat hexagonal ice crystals, some depressed in the 

 middle, or obtusely funnel shaped. 



In a paper entitled " Eine Krystallgrotte " (Groth's 

 Zeitschr. fiir KrystnUographic, \i?,%, xiv. p. 250), C. 

 A. Hering mentions and illustrates fan-shaped ice 

 crystals which probably are identical with those seen by 

 Krenner, except that they are quite flat. On the upper 

 surface of the fans some hexagonal hopper-shaped ice 

 crystals were found. 

 I VII. Condusions. — (i) Water when changing direct 

 I from the gaseous into the solid state is highly crystalline. 



(2) The tendency to crystallisation is so strong that in 

 those cases where the area of supply is limited by a wall 



I or other surface, skeleton crystals — hexagonal "hoppers" 

 I — are formed, growing away from the wall, even under 

 circumstances of excessively slow growth. 



(3) Calmness of air seems to be an essential condition 

 for their formation. 



(4) From our observations there can be no doubt as to 

 the identity of the ice crystals of Surtshellir, of the 

 refrigerating chambers and ships in Liverpool, and of 

 the cooling cellars of the Berlin breweries, with natural 

 hoar-frost. 



-Hollow Hexagonal *' Hopper" Crystals of Ice fouod in Surtbhellir. 

 (Natural size.) 



robbed of its moisture, while the edges will grow out- 

 wards, the rate depending on the amount of food 

 material. The open ends of the funnels will point 

 towards the middle of the wall-bound air-chamber or 

 cavern, or away from the wall ; in the case of hoar-frost 

 the funnels will be open towards the sky. 



FlG< 3.— Natural Hoaf-frost (Chri»tnias tBr;;;). {a and / n.-iiural size; 

 ^, f, f/, c and f; entarged.) 



This type of skeleton crystal may be termed starvation 

 crystal. 



iiy reflections from the steps seen on the triangular 

 faces of the pyramids, we were able to show that they 

 consist of combinations of faces of the hexagonal prism 

 (v. V) and the basal pinacoid (Ol')- 



NO. 1303, VOL. 50] 



THE GLACIAL SYSTEM OF THE ALPS. 



ON the day following the close of the Sixth Inter- 

 national Geological Congress an excursion, or- 

 ganised and conducted by Profs. I'enck of \'ienna, 

 Bnickner of Berne, and Dr. L. du Pasquier, left Lugano 

 to visit the chief glacial deposits of the .Alps. An excellent 

 guide-book of permanent interest, entitled " Le Systcme 

 Glaciaire des Alpes," had been prepared by theconductors 

 of the excursion. 



l)n the first day (September 17) the party, numbering 

 thirty-live, took train to Sesto Calende, and descending 

 the Ticino in boats, walked over the moraines of Lago ■ 

 Maggiore to Borgo Ticino. An excellent view of the ! 

 niorainic amphiilieatre, which forms a loop round the ; 

 southern end of the lake, and rises to 470 feet above its 

 level, was obtained from the morainic Monte del Bosco. 

 In the evening the parly proceeded to Ivrea by rail. 



Next day was spent in examining the celebrated 

 moraines of Ivrea, which testify so eloquently to the size 

 of the glacier that descended the valley of Aosia. From 

 the northern morainic ridge (the Scrra), which rises to a 

 mean elevation of 1300 feet above the central depression, 

 a good view of the great amphitheatre was obtained. 

 Late at night Milan was reached. 



On the igih train was taken to Lonato at the southern 

 end of the Lake of Garda. whence carriages were taken 

 to Salii, on the western shore of the lake. On the way 

 to Salo, most interesting evidence of three successive 

 glaciations was seen. It is found that the moraines of 

 the last glaciation show only a very thin weathered crust, 

 whereas the moraines of the two previous glaciations are 

 marked by a weathered crust called " ferretto," many 

 feet thick, in which, the pebbles, even of granite and 

 gneiss, are so much decomposed as to be readily cut with 

 a knife. The whole weathered crust has assumed a 

 deep red-brown rust colour, whence the Italian name 

 for it. 



At Mocasina the unaltered lower part of a moraine of the 

 second glaciation was seen overlying the much-weathered 

 " ferretto " crust of a moraine 01 the first glaciation. At 

 Benecco the unaltered moraine of the last glaciation 



