512 Prof. T. G. Bonney—On the Nagelflue of the Rigi, &c. 
over facts already well known to geologists, I will simply call 
attention to three points which specially attracted my notice. 
1. The pebbles of the conglomerate are not seldom indented one 
by another. These imprints, made by the more acutely curved 
surfaces of one pebble upon the less convex surfaces of another, are 
perceptible upon the harder grits, more strongly marked upon the 
softer, and most of all conspicuous upon the calcareous pebbles. 
The “pitting” of the last named is frequently very marked. I do 
not think it wholly due to pressure, but to the action of water 
localized and intensified by the pressure of the adjoining pebbles, 
while in the other two rocks the indentations are probably wholly 
of mechanical origin. 
This marking of the pebbles has been already noticed by foreign 
authors, and I should not have drawn attention to it had it not been 
for a communication made to this section last year by Prof. James 
Thomson entitled «Mention of an Example of an Harly Stage of 
Metamorphic Change in Old Red Sandstone Conglomerate.” 1? Of 
course indentation—being a change of form—is an instance of meta- 
morphic change, but the author hints at something more than this. 
It needs but a glance at the list appended by Mr. Topley to see that 
the cases adduced by Prof. Thomson are no proof of the effect of high 
temperature, or of “reduction to a plastic state,” whether by “hot 
water or hot gases.” In short, this indentation of the pebbles is 
no proof of metamorphic action at all in the ordinary sense of the 
term. No rock is perfectly rigid. The extraordinary flexures, 
gigantic and microscopic, which under pressure are produced alike 
in schists, quartzites, sandstones, limestones, slates, and shales, are. 
proof of this. No one, however, who has examined the pudding- 
stone of the Swiss Miocene or the conglomerate of the English 
Bunter (where the hardest quartzite pebbles are thus indented) can 
for a moment regard this deformation as an indication of meta- 
morphism on which the slightest stress can be laid. I should have 
not deemed it worth while to call attention to the subject did I not 
know from experience that in petrology an erroneous idea seems to 
possess a more than feline vitality. 
2. The next point to which I would call attention is the lithology 
of the nagelflue of this district. This was the point to which my 
attention was more especially directed, because of its bearing on the 
physical history of the Alps. It is probabie that the areas drained 
by the rivers of the Miocene Alps bore some relation to those which 
feed the existing streams. We may regard the conglomerates of the 
Rigi and the Rossberg as the delta of a Miocene Reuss, whose 
water system had a general correspondence with that of the present 
river and its tributaries. At least if we do not accept this view, we 
must allow a larger influence to catastrophes than is generally 
admitted by the geologists of this age. At the present time the 
upper waters of the Reuss flow almost without exception over dis- 
tricts occupied by crystalline rocks—some of these being among the 
most granitoid in the Alps. Speaking in general terms the Mesozoic 
1 See Report British Association 1882 (Southampton), p. 536. 
