1822.] Geology of Snowdon, and the surrounding Country. 405 
yielding to the knife, and much resembling some of the harder 
varieties of the rocks of Ben Glog; the direction of the cleavage 
was NE andSW. 
Beyond the village of Duygyfylche, the road rises on the ruin- 
ous side of Penmanmaur, which is so completely covered by 
fallen masses of all sizes, that we cannot assert having seen a 
single rock zn situ. These rocks have the aspect of a fine- 
grained greenstone, and consist of a greyish substance enclosing 
dark-green particles, having generally a crystalline aspect, but 
too mmute to ascertain their forms even by the assistance of 
the glass: minute and very slender crystals of transparent fel- 
spar are occasionally observable. The rock is sometimes tra- 
versed by veins of quartz, enclosing crystals of a green substance, 
much resembling those of the rock itself; and we brought awa’ 
some specimens containing the largest crystals we could find, 
in the hope of ascertaining their nature: though very minute, 
they cleave with brilliant surfaces, and afford by the reflective 
goniometer angles coinciding with those of augite. The rock 
is hard beneath the hammer, but is readily cut by the knife 
affording a grey powder ; we, therefore, conclude its chief con- 
stituents to be the substance which we have termed steatite, and 
augite, and we are the more confirmed in this opinion from hav- 
ing found one variety in which the steatite extensively prevails ; 
this yields more readily to the knife, and encloses white specks 
of a substance which, as it effervesces with acid, we conclude to 
be calcareous spar; thus evincing the connexion of this with the 
rocks before observed. 
At the termination of Penmanmawr towards Bangor, the 
appearance of this rock suddenly ceases, the hills retiring further 
from the shore, but behind Aber, we visited an old slate quarr 
where the direction of the cleavage was as usual NE and SW. 
Between Aber and Bangor, scarcely any opportunity occurred 
of observing the nature of the country, the surface consisting of 
gentle slopes, for the most part well-covered by herbage. 
The whole coast between Bangor and Conway is represented 
in Mr. Greenough’s map as consisting of the old red sandstone; 
for this rock we looked carefully, but in vain. The only rock 
that fell under our notice that could be mistaken for the old red 
sandstone is that already noticed on Conway Hill, which, with- 
out sufficient attention, might be supposed to be a conglomerate. 
From Bangor, we walked to Garth Ferry, and thence passed 
over the Menai, accompanied by Mr. Dawson and Mr. J. Woods, 
to the opposite ferry on the Anglesea side, in order to view the 
numerous trap dykes described by Mr. Henslow as occurring 
between the ferry-house and Beaumaris. The rock close to the 
ferry-house and on the shore, we assume to be Mr. Henslow’s 
greywacke, but it has to us more the appearance of quartz rock, 
consisting of crystalline grains of quartz united without cement, 
