Dr. O. Callaway—On Blake's “ Monian System.” 561 
from Sir A. C. Ramsay, who referred the whole to post-Archeean 
times. The chief difference between Prof. Blake and myself is 
that whereas I subdivide the Archeans of Anglesey into two groups, 
which, to avoid theory, I simply described as Gneissic and Slaty ; 
he desires to lump them together as one system called Monian. 
This divergence of opinion is not very serious. If stratigraphical 
links between two formations can be detected, it may (and it may 
not) be desirable to give them one name. The question is, Are 
Prof. Blake's links strong enough ? 
Before answering this query, I should like to indicate one or two 
additional points on which I am happy to express acquiescence with 
Prof. Blake. When I first studied the rocks of Anglesey, nearly 
ten years ago, I held the current views on metamorphism. Most 
geologists of that day believed that mineral banding in schists 
generally followed an original sedimentation, and the evidence then 
available tended to support that view. Accordingly, when I saw 
granite interbanded with schists in parallel beds, I followed Dr. 
Hicks and Prof. Bonney in concluding that this granite was of 
metamorphic origin. We have since then learned much of the 
wonderful effects produced by pressure. I have accordingly studied 
some of my former sections in the light of the new theories, and 
have adopted a different interpretation of some of the old facts. I 
hold that the granitoid mass in the centre of the island is truly 
igneous, and sends apophyses into the adjacent schists ; also that 
some of these schists themselves are igneous rocks, diorite and felsite, 
which have been metamorphosed by mechanical and chemical energies. 
It will be seen that I thus go beyond Prof. Blake himself, who, as 
I understand him, assigns a plutonic igneous origin only to the 
granite and the modified diorite. My views were given in outline 
to the British Association in 1887, before I knew that Prof. Blake 
had come to similar conclusions. 
How far do the new theories affect my old work? Simply thus: 
my time-succession of the Older Archewans becomes a mineral succes- 
sion. The mapping and sections remain substantially the same, 
but the element of time must be transferred from a supposed order 
in deposit to the order in which the igneous masses were extruded 
and to the period or periods of their metamorphism. 
My descriptions of the Newer Archean rocks are in the main 
accepted by Prof. Blake; but he has added many observations made 
in districts not studied by me. These, if confirmed, will prove to 
be of much interest. 
A little more care would have saved Prof. Blake some trouble. 
He elaborately attempts to refute my (supposed) opinion that the 
rocks of Paris Mountain are of Archean age. It is true that in my 
map I placed this mass in the Archean, because it was necessary to 
_put it somewhere, and the evidence seemed to me to turn a little in 
favour of the Archean view; but in the text (Quart. Journ. Geol. 
Soc. May, 1881, pp. 222 and 224), I expressly declined to assign any 
age to the rocks, and to that scepticism I still adhere. 
To return to our main question: Is there only one Archean 
DECADE III.—VOL. V.—NO. XII, 36 
