10 = Prof. Hughes—Lower Cambrian, Bethesda, N. Wales. 
_ In the talus under the cliff above Tainewyddion I found several 
specimens of Lingulella Davisiti in a grey or yellow flag similar to 
that which occurs subordinate to the Carnedd Filiast grit. We 
are here evidently in the Middle Lingula Flags, which is repre- 
sented chiefly by massive coarse grit. When we wander south into 
the district west of Arenig, there are still beds of strong grit at 
this horizon, but they are thin and quite subordinate to the flags and 
slates. The shore line was further north, and therefore in that 
direction we may expect to find the rocks of this age either repre- 
sented entirely by shore deposits or overlapped against the rising 
ground by the newer part of the series. . 
Below the Filiast grit we should search for Lower Lingula and 
Menevian, and we shall see that there are black slates about that 
horizon from which as yet no fossils have been recorded. 
#. Between Carnedd Filiast and Bronllwyd there is a depression 
which, further east, forms the head of Cwm Ceunant. This hollow is 
due te the occurrence here of a soft pale grey and white irregularly 
cleaved sandy slate. It seems to be in the line of the softer rock 
which runs through the gap between Hlidrfawr and the rocky hill 
which rises from Marchlyn Bach on the west. These slaty beds 
pass up into the sandstone and grit of Carnedd Filiast and down 
into the grit of Bronllwyd. A soft black slate is seen in this 
division above Pengareg ; any part of this series might be expected 
to yield fossils and it is here we should search for Lower Lingula 
Flags and Menevian. 
F. The grit of Bronllwyd, which comes next in descending order, 
and rests immediately upon the Penrhyn slate, consists chiefly of a 
quartz grit and conglomerate, containing fragments, generally about 
the size of a pea. It passes into banded grit and sandstone, with 
beds conspicuously mottled black and grey, the black being due 
to large mudpans, and included masses of shale pinched up in 
it, so as to occur very irregularly through what otherwise appear 
to be somewhat evenly lying beds. ‘This proves that a con- 
siderable amount of deformation often takes place even in a massive 
grit. The alteration of a grit by cleavage into a schistose quartz 
vock is well known, but this fold and fault deformation is also 
clearly a common phenomenon. 
The Bronllwyd grit is of great thickness, and rolls over rapidly to 
the south-east, a dip of 55° being observed in one place above the 
Penrhyn Quarry. 
G. The Penrhyn slates, which next succeed in descending order, 
are wonderfully uniform in character throughout, but yet a close 
observation of those small differences which affect the quality of the 
slate has called attention to slight variations of texture, as well as 
the more marked difference of colour, and enable us to make out the 
fallowing subdivisions :— 
a. Immediately below the Bronllwyd grit is a glossy light apple- 
green slate, somewhat like a hone stone in character. It is a useful 
slate, and was used for the roof of the new church at Bethesda. It 
has not been much worked, except in one quarry, known as Crimea, 
