114 
A WEEK IN NORTH WALES. 
May, 1892. 
direction. This has been, as thin sections show, very much 
crushed ; the quartz shows the uneven extinction between 
crossed nicols, evidencing a certain amount of distortion, 
and the felspars have, in several instances, been somewhat 
broken up. Nevertheless, parts of the mass, noticeable by 
Cwm-y-glo, near the foot of Llyn Padarn, show the flow 
structure very beautifully. The conglomerate, which is 
immediately over the felsite, is made up, in great part, of 
pebbles derived from it, but there are also fragments of 
various other felsites and quartzites, and the whole is set in a 
paste, composed of the fine dust of the same rocks. This 
conglomerate has also been subjected to the crushing men¬ 
tioned as having affected the compact rock, and has to some 
extent taken on a roughly schistose character. 
Mr. Harker points out that the most intense cleavage and 
metamorphism of the Welsh slates is met with just along the 
S.E. face of this old ridge of hard rock, as if the whole of the 
country had been squeezed against it. 
The walk from Llanberis to Snowdon Ranger by Maes 
Cwm has no feature of special interest until the head of the 
valley is reached, when the beautiful diversified country from 
Nantlle to Rhyd-ddu lies before us, with the magnificent ruddy 
face of Snowdon rather further round to the left. Just 
across the lake (Llyn Cwellyn) is the fine mountain mass of 
Mynydd Mawr, composed of a rock which contains a mineral 
hitherto only met with in some three other localities, viz., 
Socotra, Ailsa Crag, and Corsica. This is the form of horn¬ 
blende, called Riebeckite, containing an unusually large 
percentage of soda, and distinguished optically by its deep 
blue colour in certain directions. The changes of colour, as 
the mineral section is rotated, using the polarizer only, are 
rivalled only by blue tourmaline ; but, where the crystals 
have a prismatic habit, the deepest blue is assumed in a 
position at right angles to that which would be the case with 
tourmaline. 
Our time only allowed of a rush to the hill, a hurried 
collection of a few specimens, and a rush back to the station 
to catch the train for Rhyd-ddu en route for Beddgelert. 
The Snowdon Ranger Station presents a considerable 
contrast to New Street Station. There appeared to be one 
official, and he, very sensibly, was that day filling up the wide 
gaps in his duties by haymaking in the field which adjoined 
the line. The train was late (it was Bank Holiday), and yet 
it seemed to come too soon, disturbing our quiet rest on the 
grassy bank of the little station, in full view one way of the 
quiet lake, and in the other of the grand mass of Snowdon, 
with his precipices, buttresses, and peaks. 
