58 Prof. T. G. Bonney—Rounding of Alpine Pebbles. 
1 foot diameter. Mostly granitoid gneisses of a somewhat friable 
character. 
I have in my note book observations of the Inn at Jenbach, Inns- 
bruck, and near to Landeck, of the Isel between Windisch Matrei 
and Lienz, of the Drave at the latter place, of the Hisack near 
Brunecken, and at Bozen, of the Romanche at Vizille, and the Isére 
at Grenoble; but it is perhaps needless to quote them in detail, as 
to a great extent they would be repetitions of the above statements. 
Suffice it to say the stones commonly range from about 8 ins. to 6 ins., 
smaller and larger occurring, in the latter case not seldom up to 
nearly 1 foot, with occasional large boulders; that the amount of round- 
ing is variable, but the majority of the first named may be described 
as from subangular to moderately rounded —well-rounded pebbles 
being generally not common.' Materials, Alpine rocks with variable 
amounts of limestones and grits. At Bozen also the igneous rocks 
of the district were well represented. 
Group III. 
The first case examined was the Po at Turin. The river and its 
tributaries have now flowed over about 85 to full 50 miles of plain. 
The principal streams which feed it descend valleys from about 15 
to over 30 miles long, and may be reckoned as having their sources 
at from 5000 to 6000 feet above the sea.” 
The stones exposed near the banks consist chiefly of Alpine rocks, 
are commonly 3 ins. to 4 ins. diameter, occasionally running up to 
about 8 ins. together of course with smaller. As a rule they are not 
well rounded, retaining more or less a subangular outline, though 
the corners and edges are worn off. 
In travelling from Turin to Milan, and thence to the Lago di 
Garda, several rivers are crossed, and sections obtained of the sub- 
stratum of the great alluvial plain of Piedmont and Lombardy. The 
results in regard to the former may be summarized in a tabular form. 
Approximate length of river. Diameter of Pebbles. 
Name. Condition. 
Among the Mts.| Over the plain.| Average. | Maximum. 
Stura ...| 18 miles. 20 miles. Sito) 4a p6"|  rhay GC Bee 
Orco...... 2201, 1 Site abt. 4” 6” | Fairly well rounded. 
Sesion i265 Be. abt. 2” |rarely>4” | Moderately __,, 
Ticino ... aN 202 3” to 4” p » ” 
Adda’ °.. te PAD 3” to 4” 26’ | Fairly well a5 
The main streams of the Ticino and Adda have most of their 
Alpine pebbles stopped by the Lakes of Maggiore and Como, but 
* Our estimates of the rates of flow varied from about three to four and three- 
quarter miles an hour. I expect these great mountain rivers run at an average pace 
of nearly four miles an hour, and at certain seasons considerably exceed this. 
* I mean as fairly strong streams; in some cases brooklets would be higher, and _ 
of course the snow-beds about the sources of the Po rise up in places to quite 
9000 feet. 
