Prof. T. G. Bonney—Rounding of Alpine Pebbles. 57 
Well-rounded pebbles rare, and never large. Alpine rock, including 
some serpentine. 
Little plain at foot of Gross Venediger.—Enclosed by cragg 
mountains ; stones brought down by various torrents, chiefly from 
snow-beds and glaciers, descending precipitously from 1000 to 2000 
feet. Boulders and pebbles of Alpine rock, the latter not much 
rounded, having generally little more than the corners worn away ; 
only some of the smaller and softer are moderately rounded. 
Bed of Stillupthal (Zillerthal).—Glaciers and snow-beds surround 
the head of the valley, the floor of which rises rather gradually. 
Deposits torrential in character. Alpine rock. Observation at 3500 
feet, where the stream flowed with only a slightly broken surface. 
Stones subangular to imperfectly rounded, mostly 3ins. to 4 ins. in 
diameter, a few nearly afoot. A couple of miles or so lower down, at 
a height of 2950 feet, the flow is more rapid: many pebbles 3 ins. 
to 4ins. in diameter, varying from rounded subangular to subangular 
rounded, together with larger boulders of all sizes up to at least 
a yard diameter, some of which were moderately rounded ; chiefly 
gneiss and granitoid rock. 
Below Ginziing, Zillerthal.—Place of observation about 8230 feet: 
the river being formed by confluence of a torrent from the Floiten- 
thal (a glen about nine miles long, enclosed by steep mountain walls, 
seamed by cascades and rising at the upper end from 9000 feet to 
11,000 feet, and terminated by a rapid descent through a rocky 
gorge) and that from the Zemmthal (a valley perhaps three miles 
longer, which rises on the whole more gradually, and is enclosed 
by mountains somewhat lower). Materials, various Alpine rocks. 
All sizes up to about a foot in diameter common, but many exceed this ; 
blocks up to two or three feet diameter not being rare: much variability 
in the amount of rounding, many being quite subangular, but some 
fairly well rounded,! these chiefly a rock resembling a tonalite not 
rich in quartz and a felspar-actinolite rock (rather rare). The 
former I believe occurs in situ far back in both these glens. 
Group II. 
We may commence by following the course of the river last 
described. At Mairhofen (2096 feet) by the Calvarienberg, stones 
commonly 4 ins. to 6ins. diam., but both smaller and larger, are 
present; some blocks are quite a yard in diameter. Amount of wearing 
very variable ; almost the only well-rounded pebbles are the above- 
named ‘tonalite’; next to that is a porphyritic gneissoid rock, 
common in the Stillupthal. Alpine rocks, with some subcrystalline 
limestone. 
At Zell (four miles and a half and more than 200 feet lower down). 
Stream strong, surface rather broken in the swifter parts. Stones 
mostly from rounded subangular to fairly rounded, commonly from 
about 4ins. to 6 ins. smaller of course occur, but rarely one over 
1 It must be remembered that when a torrent descends precipitously over a bed of 
rock, not a few stones may receive an exceptional amount of rounding by being 
whirled about in ‘ potholes.’ 
