Dr. C. Callaway—On Blake’s “ Monian System.” 568 
to me quite unsuccessful. I will give two examples. In the 
Llangefni “‘syncline,” Prof. Blake wishes to construct a sequence 
from the grey gneiss up to the Llangefni conglomerates. He admits 
a fault somewhere to the east of the gneiss ; but says that “the throw 
of the fault may* not be great, and the lowest rocks exposed (to the 
east of the fault) may not be far above the grey gneiss.” Again: 
the rocks to the east of the fault pass downwards into the Llangefni * 
conglomerate ; but Prof. Blake comes to the conclusion that this order 
is inverted, and he offers as his main proof the proposition that if 
there is no inversion, the order is different from that which obtains 
elsewhere. But I am not at all satisfied what is the normal succes- 
sion, and I do not think that Prof. Blake has established it. In this 
district, then, Prof. Blake’s demonstration rests upon two hypotheses 
and an unproved inversion. 
Again, in the area south-west of Mynydd Llwydiarth, our author 
is “led to see there is an undisturbed succession” between my 
Gneissic and Slaty groups, although he admits that the ground is 
“broken.” It is broken, with a vengeance, and any attempt to 
mend it into ‘“‘an undisturbed succession” is doubtful in the extreme. 
If Prof. Blake’s “Monian System” is of any value, it must be 
applicable to other regions. Its author applies it to Shropshire. 
The Longmyndian* group is referred to ‘“‘Upper Monian”; the 
Uriconian and Malvernian are lumped together as ‘‘ Middle Monian.” 
The Longmyndian is placed in the “ Upper Monian,” because it is 
correlated with the Bray Head Series (elsewhere affirmed to be 
Upper Monian) by its fossils. This fossil evidence is entirely new 
to me. When we have seen it, we shall be able to judge of its 
value. As the Longmyndian is largely derived by denudation from 
the Uriconian, there must be a considerable gap between the two. 
Again, there must be a marked break between the Uriconian and the 
Malvernian, for the latter underwent its metamorphic change (by 
whatever means) before the Uriconian period, and its dominant strike 
is discordant to that of the newer series. And if the Malvernian 
is only ‘Middle Monian,” where shall the “Lower Monian” be 
found? But to those who know the Shropshire rocks, the attempted 
correlations will appear so unsubstantial that any argument I can 
urge will almost seem like beating the air. 
If the Longmyndian is Archean, Shropshire and Malvern will 
furnish us with a threefold subdivision of the Archean rocks, the 
Malvernian, the Uriconian, and the Longmyndian ; and I submit that 
these will make far better types than the battered fragments of 
Archean rock in Anglesey. If the Uriconian is Pebidian, of course 
Dr. Hicks’s term has priority. 
' The italics are mine. 
2 Prof. Blake calls this an ‘‘agglomerate.’’ As the contained fragments, which 
are rounded, are mainly quartzite, with grits and hornstone in smaller proportion, I 
do not see the applicability of the term. 
5 I used this name for the Longmynd series in a paper contributed to the Trans- 
actions of the Shropshire Archeological Society in 1887, on the ground that its 
Cambrian age was doubtful, 
