670 DR. C, CALLAWAY ON THE [Nov. 1902, 
north-westward, and this appears to be the dip at Tai-newydd, a 
third of a mile to the north-north-east. Clear north-westerly dips 
are seen to the south-east of Clegyr-gwynion ; but a little farther 
north, around Treferwydd, and in the old quarry south-east of Tre- 
ferwydd, the dips are only slightly to the west of north. North- 
westerly dips, however, appear in force to the south-east of Llech- 
cynfarwy, and the same dip occurs at Rhén-blas, still farther to the 
south-east. 
A furlong east of Rhén-blas, near Pentre’r-felin, hornblendic 
gneiss crops out at several points with dips to north and north-east, 
In one quarry, the foliation-strike curves round, so as to give 
these and the intermediate dips in the same visible mass. We are 
here at the north-eastern end of the ellipse, for granite comes in 
immediately to the north-east ; and close by, to the east, the gneiss 
begins its easterly dip. 
From the last point, we follow the south-eastern side of the 
ellipse. East of Gwyndy, there is a fine section of the gneiss, 
apparently plunging to the east-south-east below the granite. 
Exposures then become rare, until we approach the Craig-yr-Allor 
area. Here the outcrops of gneiss and granite are almost countless, 
North and north-east of Clegyr-mawr, the dip is usually a little to 
the south of east. Around Craig-yr-Allor, it is sometimes east or 
even a little to the north of east; but, as we come round towards 
our starting point, it becomes east-south-easterly and finally south- 
easterly, thus connecting with the south-south-easterly dips on the 
Holyhead Road. The angle of dip in this series of sections varies 
between low and high; but the majority of them are described in 
my note-book as ‘ moderate,’ that is, from 40° to 50°, 
Within the ellipse, towards its north-eastern end, is an area in 
which the gneiss is contorted, with strikes deviating not much from 
east and west. These are seen at Treferwydd and at several points 
to the south, as far as Tai-newydd. Ido not know whether they 
are continuous across the ellipse by way of Llandrygarn; but east 
of that hamlet and north of Gwyndy, east-and-west strikes are 
common. I have never observed these strikes reaching as far as the 
marginal junction with the granite. 
Granite appears sporadically in masses within the Craig-yr-Allor 
ellipse ; but itis not necessary to my purpose that I should anticipate 
Mr. Greenly’s expected map. My paper, however, would be hardly 
intelligible without an outline-map, which also includes the acidic 
rocks to the east of the ellipse (fig. 1, p.664). It will be seen from 
the dips inserted in this map, that the foliation in the dark gneiss 
indicates a domical structure, and that at the margin the dips are ™ 
uniformly in the direction of the surrounding granite. 
(b) The foliation of the dark gneiss.—I have retained 
the descriptive term ‘ dark’ before ‘ gneiss,’ because the colour is 
due to more than one cause. Itis usually produced by the presence 
of either hornblende or biotite, but frequently chlorite appears in 
abundance. Epidote and iron-oxide are sometimes present. 
