Prof. I. G. Bonney—On the Nagelflue of the Rigi, &e. 5138 
rocks which inclose the famous Bay of Uri terminate at the Mader- 
anerthal on the right and at the Maienthal on the left bank of the 
Reuss. Thus the pebbles of the Reuss valley are largely made up 
from crystalline rocks. Alpine schists and gneisses abound in the 
erratics which are scattered along the flanks of the Rigi on either 
side to a height of about 5500 feet above the sea. I was anxious to 
ascertain to what proportion these rocks entered into the conglomerate. 
While travelling from Lucerne to Schwytz by the new railway I 
thought that I saw a few pebbles of gneiss in the conglomerate 
blocks built into walls above the Lake of Zug, but satisfied myself 
that if present they were far from common, and that grits and lime- 
stones predominated. When I was able to search the Rigi more 
carefully, I did not meet with a single pebble of schist or gneiss 
either between Weggis and the Rigi-kulm, or between that and 
Goldau. In the débris of the Rossberg I found, after searching for 
nearly two hours, three pebbles of a greenish schist, obviously one 
of the most modern among the crystalline rocks of the Alps, and one 
(extremely decomposed) of coarse Alpine gneiss. With the ex- 
ception of a granite. presently to be noticed, the great mass of the 
conglomerate consisted of a variety of grits, sometimes coarse, more 
often fine, sometimes almost a quartzite, sometimes ordinary hard 
sandstones, and of limestones, pure and impure, light and dark; con- 
sisted in short of a great variety of rocks representing the Mesozoic 
and perhaps the early Kainozoic deposits of the Alpine region. There 
are occasional pebbles of chert, both dark and reddish-coloured. 
Vein quartz is very rare, if not absent. ‘The one exception is a 
number of pebbles of a granitic rock. These were not noticed by 
me till I got some distance above Weggis, but they occur over the 
other parts of the mountain which I traversed, including the descent 
to Vitznau and the conglomerates by the lake shore between it and 
Weggis, and in the débris of the Rossberg. They vary in their 
proportion to the others; commonly I should say they form not more 
than 1 or at most 2 per cent. of the whole, but now and then, 
especially on the northern side of the Rigi, they amount to 5 per cent., 
and in one case I counted eleven exposed in about a square foot of 
stone (the largest being a little over two inches in diameter). The 
rock is a moderately coarse granite, consisting mainly of whitish 
quartz and reddish felspar, with a variable small quantity of a dull 
green mineral, decomposed black mica or hornblende. Occasionally 
we find specimens of a compacter and more porphyritic rock, either 
a “quartz-porphyry” or “ granite-porphyry ” of continental writers ; 
probably, however, this is from the same region as the other rock. 
These granites are totally unlike any Alpine granite or protogine 
known to me; but there is a small quantity of granite on the 
Bristenstock and a ‘‘ red porphyry ” on the Windgelle which I] have 
not seen. Jam not aware that Swiss geologists have succeeded in 
identifying the sources of these pebbles any more than of the blocks 
of the Habkerenthal. 
The lithological character of the nagelflue then entitles us to 
assume that at the time of its deposition the rivers which drained the 
DECADE II.—VOL. X.—NO. XI. 33 
