J. H. Marr—Origin of Archean Rocks, 2a 
p. 637), viz. that “‘the rocks have a general stratified structure, 
but the individual beds often present great irregularities of thick- 
ness, being specially prone to lenticular development,” is quite 
explicable if we suppose they were volcanic products, but otherwise 
is only accounted for on the supposition that they were all shallow- 
water deposits, which seems somewhat improbable. 
3. The rapid accumulation of great masses of volcanic matter 
would cause the first formed outpourings to become deeply buried, 
so as to be brought within the influence of metamorphic action, 
whether produced by heat, pressure, and water, or by intrusion of 
granite and other plutonic rocks, or by both causes. The metamor- 
phosed rock becoming denser, would contract, and cause puckerings. 
4, At first, as volcanic activity was more violent, denudation could 
not take place so rapidly as accumulation, but as the volcanic forces 
died out, the intensified denuding forces supposed by Prof. Darwin 
to have been brought into play would remove much of the accumu- 
lated material, lay bare wide areas of the once deeply buried rocks 
which had become greatly metamorphosed, leave here and there 
some rock only partially metamorphosed, but remove all or nearly 
all the unaltered rocks at the top, and would carve out the system 
of hill and valley described in a former part of the paper. On these 
hills glaciers might be formed. 
o. As this great denudation removed large masses of rock, it would 
again relieve the pressure, and some of the quartz felsites intruded 
in the newer Archean rocks might be thus permitted to force their 
way up, and perhaps give rise to those comparatively unaltered 
rhyolitic rocks and ashes which occur at the summit of the Archean 
rocks in some places. 
6. We know that volcanic areas have a tendency to subside, on 
the dying out of volcanic activity. For this reason (and also because 
the rapidly denuded materials of the land would be washed into the 
scar left by the moon’s separation, and tend to fill this up), the 
seas would gradually encroach upon these irregular Archean lands, 
and so the Cambrian rocks would commence at different times to 
be formed against different levels of this subsiding land surface, 
generally being formed sooner in the west of Hurope than in the 
east, as explained by Dr. Hicks in a paper already referred to, but 
the oldest of these rocks in Europe being always of comparatively 
local distribution, because they were deposited in wide submerged 
valleys, whilst the intermediate mountain ridges received no deposits 
at that time. 
The terrestrial and volcanic origin of the Archean rocks, if it 
can be maintained, would dispose of most or all of the difficulties 
hitherto discussed. The great difficulty in the way of the ordinary 
metamorphic theory of these rocks, namely; the wide-spread oc- 
currence of regional metamorphism in Archean times, and its rarity 
in later times, is accounted for, as similar metamorphism would be 
going on at later periods, but the exceptional violence of denudation, 
and its long continuance, would explain the exposure at the surface 
of so much Archzean rock altered at a great depth. This exceptional 
