Prof. T. G. Bonney—On the Nagelflue of the Rigi, &e. dil 
spersed earthy dust, minute micaceous minerals have been formed, 
and the free silica been deposited as chalcedonic quartz or perhaps 
sometimes opal—and as the result a rock is produced to the eye 
indistinguishable from one of those formed from similar mineral 
matter much more finely divided. 
In conclusion, I will venture upon two remarks. One, that no 
inferences with regard to metamorphism can be accepted until they 
have been fully confirmed by the evidence of the microscope, and in 
this particular branch of investigation the observer must be contented 
to serve arather long apprenticeship. The other, that in the Val Orsine 
conglomerate we have distinct proof that the principal Alpine meta- 
‘morphism occurred long before the Carboniferous period. When 
that conglomerate was deposited, the rocks from which it was 
derived and on which it rested were schists and gneisses not 
materially differing from those which now form the great central 
masses of the Alps. Go where you will in the Western, Central, 
and the greater part of the Hastern Alps (for of all these I can 
speak from personal knowledge), you pass abruptly from the com- 
paratively unmetamorphosed rock, whose age you know, to a highly 
metamorphosed rock, of which you can only say that it is immensely 
older. Further, in the latter series you can trace a certain litho- 
logical and stratigraphical sequence, which leads upwards through 
a series of groups, how far separable I will not now attempt to say, 
from the coarse granitoid gneisses and protogines to the topmost well- 
stratified, but still truly metamorphic, schists; so that we seem 
justified in demanding very clear evidence before we can accept any 
of the crystalline foliated rocks of the Alps as of Devonian or ~ 
Silurian age, even if we carry the latter group to the lowest limit of 
the late Sir R. Murchison. 
ViI.—Notr on THE NAGELFLUE oF THE Rict anp RossBera.! 
By Pror. T. G. Bonnuy, F.R.S8., F.G.S. 
HE remarkable conglomerate, called nagelflue, which fringes 
a considerable extent of the northern district of the Swiss Alps, 
and in places forms almost mountain masses rising some 5000 feet 
above the sea, has already received much attention from geologists. 
One might then fear to handle a subject almost as well worn as its 
pebbles. Still there are one or two points to which in the present 
state of our knowledge it may be worth while to call attention. 
During the last quarter of a century I have frequently passed over 
the beautiful sub-Alpine district of Switzerland in which the nagel- 
flue and the molasse are the dominant rocks, the former affording 
the bolder, the latter the gentler scenery of the region; but last 
summer I devoted three or four days to a special examination of 
the great masses of nagelflue in the neighbourhood of the Rigi. I 
examined this mountain on both sides, and spent some time in 
investigating the vast blocks which fell from the Rossberg and 
overwhelmed the ill-fated village of Goldau. Without lingering 
1 Read before Section C, British Association, at Southport Meeting, 1883. 
