326 Messrs, W. Phillips and S. Woods on the [Nov. 
still incline to green, though the absolute surface is a greyish- 
white, and its structure is in some degree slaty. It contains, 
besides felspar, masses of a white substance, which in the inter- 
nal part of the rock are translucent, when weathered white and 
opaque ; these have much the aspect of hornstone, and often 
inclose crystals of quartz in their cavities ; they scarcely yield 
to the knife; they vary in size from half an inch to six or seven 
inches in diameter; and they appear to us to consist of the same 
material as the rock itself, but include a far greater proportion 
of siliceous matter, and we believe them to be of contemporane- 
ous origin with the rock inclosing them. 
The slates of the middle region of the mountain occasionally 
do not differ in their external characters from ordinary slate, 
but by transmitted light through the thin edges, they often, 
though not always, appear of a green colour. These slates, as 
well as the rocks, frequeutly contain small cubic crystals of iron 
pyrites. 
The rocks of the upper third all partake largely of the aspect 
of steatite, which, though it may be said to form the imbedding 
substance or paste, has often a crystalline aspect, and is always 
porphyritic from its containing distinct macled crystals of trans- 
parent felspar, opaque calcareous spar which effervesces with 
muriatic acid, and prismatic crystals of a blackish-green augite, 
affording cleavages sufficiently brilliant for the use of the reflec- 
tive goniometer; the rock is generally of a greenish colour, 
which is much heightened by the addition of moisture, and the 
examination of it in that state discovers the presence of a multi- 
tude of minute particles (probably of chlorite) of a much brighter 
green than the augite, and to which the green colour of the rock 
may be attributed. These rocks are of considerable hardness, 
often very hard, and they suffer so little from exposure, that the 
weathering has scarcely proceeded to the depth of one-fourth of 
an inch into the solid rock, and we could easily distinguish this 
upper rock by a peculiar external roughness. It returns a ring- 
ing sound, when struck by the hammer. 
But although the rocks abovementioned prevailed each at 
different elevations, further investigation proved that the slates 
of the middle, and the steatitic rocks of the lower region, are 
frequently interstratified: this was observed in very many 
instances in crossing the eastern side of the mountain at a con- 
siderable elevation, and again very frequently on the side of the 
road near Pont y Cyflin at the eastern foot; but in no mstance 
did we observe the rocks of the summit so circumstanced. 
Near Pont y Cyflin likewise we clearly perceived several in- 
stances in which the same rock as that prevailing at the base of 
Moel Shabod, passes into a greenish slate, which is soft and 
granular, 
But it must be remarked that this interstratification of the 
