J. HE. Marr—Origin of Archean Rocks. 267 
in various parts of Hurope, and the absence of large pebbles in the 
basement beds of different age in many other parts of Europe. The 
large boulder conglomerates would be formed where Boulder-clay 
was found to supply the pebbles. 
Another illustration of the irregularity of the Archean land- 
surface is still more difficult to explain by irregular earth-movemeuts, 
but presents all the appearance of a large submerged valley. This 
is furnished by the distribution of the stage C’ in Bohemia. The 
beds of this stage are found at Skrey on the north side of the basin 
of Lower Paleozoic rocks, and at Ginetz on the south side, and they 
rapidly die out in an east and west direction at both these places. 
They rest upon conglomerates and sandstones, whereas in other parts 
of the basin the conglomerates and sandstones of stage D rest upon 
Archzan rocks, so that a section across this part of the basin before 
the disturbance of the Cambrian rocks would be somewhat as shown | 
on Figure 2. 
(Fic. 2.) 
ee ———————————————————EeEEEEEEEEEEEEee 
See een 
SS SS ———————— 
——— ————— 
————— ——————— 
——— i ———————— 
eS Ee 
Se 
= ee 
I ———— 
LSD ea = Sao 
yj, LOA SS SAMO RED SSS 
ROA Gh ten Ae Sas 
a 
Archzan Rocks. 
The dotted part indicates shore deposits. 
The beds of stage C extend for a distance of about thirty kilo- 
métres on the north side of the basin, and a little less than this on 
the south side, and the deposits of C, and the underlying sandstones 
and conglomerates are many hundreds, and probably thousands, of 
feet in thickness. It seems that here a large valley was submerged 
in Cambrian times, and that the valley was one of denudation, and 
not produced by earth movement, for the direction of the depression 
is about at right angles to the direction of strike of the Archean rocks 
in which it occurs. 
From all these considerations, it would seem to follow that an 
enormous amount of denudation took place at the end of Archean 
times, quite sufficient to bring to the surface great masses of rock 
which were metamorphosed at a considerable depth below it. 
o. An abnormal amount of volcanic activity appears to have 
occurred during Archean times. Where the rocks are comparatively 
unaltered, the volcanic rocks are readily recognizable, as at St. 
Davids, Bangor, the Wrekin, and other places (cf. papers by Messrs. 
Hicks, Hughes, Bonney, Callaway, and others in the Geological 
Society’s Journal), and it seems to be recognized more and more, 
that some at least of the highly altered rocks are also of volcanic 
origin. Professor Bonney, for instance, speaks of certain Cornish 
hornblende schists as possibly ‘‘having been basaltic tuffs with 
which in chemical composition they would agree fairly well” (Quart. 
Journ. Geol. Soc. vol. xxxix. p. 19). Mr. Reusch also (Silurfossiler 
og Pressede Konglomerater i Bergenskifrene) considers that the 
