©‘ Ash-bed’ and ‘ Bala Limestones.’ 345 
whole course of which I once had an opportunity of examining 
the various layers composing it; and we were able to do the same 
thing again by means of the débris on the outside. 
Here are fissured blocks of rapidly decomposing Feldspar, the 
parent beds of which may have furnished materials for some of the 
fine clays of the overlying. formations. ‘There are others made up 
of angular fragments of red and white Feldspar, set in a greenish 
paste, extremely hard: so large are some of the red fragments, that 
a miner once brought me a piece he had found in an ancient drift- 
bed overlying one of the Coal-seams as a proof of the existence in 
those days of men who knew how to burn bricks and pottery! In 
many of the fragments lying about, we saw how the coarser layers 
pass gradually into a finer texture of hard grey and green beds, in 
some of which are large crystals of sulphate of iron, embracing 
every variety of compactness, together with shaly and imperfect 
slaty cleavage; and if we were to follow the course of this Ash-bed 
two miles to the north, where it is thrown up into the ruggedly 
grand escarpment above Pontymeibon, we should see these various 
layers with their alternations and gradations zm situ, and we should 
also observe how the whole series is traversed diagonally and per- 
pendicularly by great veins of quartz. In accounting for the origin of 
Ash-beds such as this, some have supposed them to be made up of 
volcanic matter thrown up and deposited under water; but while we 
can conceive of a layer of limited extent geographically deposited 
in this way, the vast extent of country traversed by this and its 
neighbouring Ash-beds, their great thickness, and the preservation 
of their structural characteristics along their entire course, lead me 
to look with more favour to the theory which regards them as the 
‘recomposed’ detritus of older igneous rocks, regularly deposited, 
and afterwards subjected to the consolidating influences of heat and 
pressure. ‘The one we have been examining is the lowest of three 
Ash-beds which in North Wales underlie the Limestones, Sand- 
stones, and Shales forming the variously designated Bala, Llandeilo, 
or Caradoc group of rocks; below it we find a dark-blue rock 
plentifully dotted with iron pyrites—then a thin band of Greenstone, 
a true igneous rock, and then a thick zone of dark earthy slates. 
Below this, in this part of North Wales, we cannot go, because the 
beds described in this paper, though rolling over in numerous 
bends and dislocations, keep to the surface and hide the inferior 
strata from view ; but if we were to follow them northwards towards 
the lake and town of Bala, we should observe the dark Shales and 
Slates finally resting upon the Ffestiniog rocks, which in their turn 
conduct us down to the Tremadoc Slates and Lingula-flags. All 
this, by the way, as turning NE. from the farm-house, we made 
for Nant Iorweth—a dingle which opens into Glyn Ceiriog. Before 
long the loose blocks of Quartz and pale-green fragments of Ash 
which strew our path tell us we are crossing the second of the Ash- 
beds, which differs somewhat from the first in the preponderance of 
hard pale-green and greenish-white beds, together with dark grits. 
This band may be studied to advantage where the romantic glen of 
