J. BH. Marr—Origin of Archean Rocks. 269 
the conditions under which the Archean rocks were produced were 
somewhat different from those under which later rocks were produced, 
and this difference may have been very great. What actual evidence 
have we, then, of marine or fossiliferous rocks of Archean age? The 
cases usually cited are :— 
(i.) Crystalline limestones, some containing Eozoon. 
(ii.) Beds of graphite. 
(i1i.) Beds of haematite. 
As to EKozoon, we know that “ doctors disagree,” and it can hardly 
be brought forward as an argument in favour of the marine origin 
of the rocks in which it occurs, if other facts are opposed to this. It 
1s unnecessary to quote the numerous authorities who are opposed to 
the organic nature of this structure. 
With regard to the rocks themselves, these facts are worthy of con- 
sideration :—The crystalline limestones appear to be mainly lenticu- 
lar masses of small extent. This is the case in all areas where the 
writer has had an opportunity of examining them. The presence of 
these very lenticular patches and the absence of wide-spread beds of 
limestone would point to this rock not having originated in an 
Archzan sea, but in some other manner, as by precipitation from 
calcareous springs, such as are found in most voleanic districts. 
The graphite also has been appealed to, as proving the former 
existence of organisms, but we know that graphite is also formed 
under other circumstances. It is found disseminated as scales, as - 
well as occurring in pockets in the Borrodale beds of the Lake Dis- 
trict ; it occurs in the same way in Bohemia, not only in apparent 
or real layers, and pockets, but also disseminated as scales in the 
eneissose rocks, forming in places actual graphitic gneisses. The 
hematite is supposed by Dr. Sterry Hunt to have been produced by 
precipitation of iron by vegetable matter ; in these same Borrodale 
beds, we meet with masses of hematite, which could hardly have 
been formed by filtration from rocks above them. Certain white 
flinty rocks occurring among the green schistose rocks in Bohemia 
bear a striking resemblance to siliceous sinters, but this may be only 
superficial. 
These rocks, then, need not necessarily have been formed in the 
sea, as similar rocks are formed on land, in volcanic regions. 
Furthermore, the different varieties of rock do not occur in the same 
relative abundance as one would expect, if they were ordinary 
marine sediments which had been subsequently altered. In all 
newer systems we find great masses of limestone somewhere or 
other, e.g. the Cambrian limestones of Russia and Eastern Sweden; 
the Silurian of Russia, Sweden, Bohemia, Niagara, ete. ; the Devonian 
of Devonshire, and the Hifel; the Carboniferous of Western Europe ; 
the New Red of the Alps; the Jurassic and Cretaceous of Western 
Kurope; and the Tertiary of Europe, the Himalayas, etc. In the 
Archean rocks, on the other hand, although such large areas are 
exposed, we never seem to get large masses of limestone, but merely 
these lenticular patches. A glance at the Geological Survey Map of 
Anglesey will show the great contrast which these Archean lime- 
stones show to other limestones. 
