268 J. LE. Marr—Origin of Archean Rocks. 
gabbros, diorites, dioritic schists, hornblendic schists, and other 
metamorphic rocks of the Bergen district, are altered tuffs and 
eruptive rocks. He gives two alternatives as to their age (p. 105), 
one that they are Silurian, and interstratified with the somewhat 
altered fossiliferous rocks; the other, that they are inverted anti- 
clinals, with the fossiliferous rocks occurring as synclinals between 
them. In either case, they seem to give evidence that regionally 
metamorphosed rocks of similar character to those found in the 
Archean systems may be produced by the alteration of possible 
volcanic rocks. Whilst alluding to this work of Mr. Reusch, it 
may be further noticed that great interest attaches to the fossils of 
Silurian age occurring in such highly altered rocks as those described 
by Mr. Reusch. When we hear of fossils preserved under these 
circumstances, it is noteworthy that the limestones in the Archean 
rocks, which have been examined so carefully, have yielded nothing 
more satisfactory than the dubious Eozoon. Professor Heddle, in 
his descriptions of “the County Geognosy and Mineralogy of 
Scotland” concludes that among the most metamorphic rocks of 
Sutherland is a series of contemporaneous volcanic sheets. 
The occurrence of so much volcanic matter, so widely spread 
among the Archean rocks, is difficult to explain, if we suppose that 
the great bulk of the Archean rocks was formed under conditions 
similar to those under which the ordinary fossiliferous rocks were 
produced. 
6. The Archean rocks present many peculiarities which it is 
exceedingly difficult to explain, if they be considered as marine 
deposits, whereas many at any rate of the types found might be 
produced by the alteration of ordinary pyroclastic rocks. The 
Cornish rocks do not appear to have yielded to Prof. Bonney’s 
searching microscopic examination any convincing proofs of their 
marine origin, for in a footnote on p. 19 of the paper referred to 
above he says, ‘‘ While examining this hornblendic group I had 
always present to my mind the possibility that the more massive 
varieties might be really metamorphic igneous rocks, but I obtained 
no evidence in favour of this view, and am disposed to regard the 
group as, at any rate in the main, of sedimentary origin.” The 
cautious way in which Prof. Bonney speaks of them would seem 
to allow of the possibility that they may be of pyroclastic origin. 
Many of the green schistose rocks would appear to be of such a 
composition as is quite in accordance with their pyroclastic origin, 
but when we remember the difficulty of distinguishing in some 
cases a comparatively unaltered pyroclastic rock, from the grits 
derived from the denudation of such rocks, it will prevent us from 
laying much stress upon this point. However, if so many Archean 
rocks can be proved to be of volcanic origin, it is quite as legitimate 
to conclude that others also are of volcanic origin, where the original 
nature is nearly obliterated, as to suppose that these latter are marine 
sediments, unless we can point to undoubted marine sediments in 
the Archean rocks. Once granted that volcanic action was more 
powerful in Archean times than in later times, and we admit that 
