Correspondence—Dr. Callaway. 95. 
The schist in the Llanfechell Grit is not of volcanic origin tanquam 
schist ; it must have originated as rock, and been metamorphosed into 
a schist, before the orit was deposited. The metamorphism must 
have taken place at some depth, and there must have been a period 
of denudation previous to the exposure of the schist at the surface. 
His examples of the conglomerates of Llangefni and some of the 
Bangor beds are not to the point; since the fragments derived from 
the associated beds are volcanic, and contemporaneous denudation in 
volcanic rocks is common enough. That the ‘conglomerate of 
Moel Tryfaen is largely composed of the immediately preceding 
Cambrian slates” I dispute. I have seen this conglomerate on 
Llyn Padarn, and I followed it all along the crest of Mynydd y 
Cilgwyn, but not a bit of Cambrian slate did I find in it. Dr. 
Hicks studied it in the intermediate ground of Moel Tryfaen with- 
out finding slate. I therefore venture to reject all Prof. Blake’s 
supposed parallel cases, and I call upon him to prove that a true 
erystalline schist could have been included as a derived fragment in 
a (roughly) contemporaneous sedimentary formation. 
As to Llyn Trefwll, I am quite aware that a large part of the 
ridge close to my sections consists of basic igneous rocks; but as 
they had no bearing upon my work, I have not referred to them. 
The rock zn situ, which Prof. Blake now admits is a true slate, on the 
authority of Prof. Bonney, contains rounded pebbles of the adjacent 
granite; and Prof. Blake has no right to say either that I mistook 
diabase for slate, or that I sent. to Prof. Bonney certain derived 
fragments in mistake for rock in situ. 
I am sorry the two examples of a supposed passage between the 
‘lower and upper groups,’ which I selected because they happened 
to turn up first, prove to be bad ones. Perhaps Prof. Blake would 
consider his succession in the northern area more satisfactory. If 
so, I do not think he will mend matters. He makes the Llanfechell 
Grit to overlie the schists of Mynydd Mechell; but there is more 
reason to believe that they are one and the same set of beds in 
different stages of alteration. 
Prof, Blake has disappointed me. I asked for particulars of the 
fauna by whose aid he correlated the Longmyndian with the Bray 
Head Series, and he refers me to Arenicolites didyma! 1 supposed I 
must have overlooked some important palzontological discovery ; 
but no, our familiar little friend turns up in immortal bloom! I 
respect Arenicolites for its antiquity, but as a time indicator it is 
worthless. : 
The “Malvernian” rocks, which I said were included by Prof. 
Blake in his “ Middle Monian,” are called by him “the granites and 
altered rocks of Primrose Hill.” I do not think any one who knows 
the region disputes that these masses are approximately of Malvernian 
age. 
Prof. Blake dwells upon the consequences of my acceptance of the 
igneous origin of the hornblende schists. I stated those consequences 
unreservedly in my ‘ Notes,” and I do not feel a bit ashamed that I 
worked on the accepted principles of our science, and was not able 
