The Glyder Range
Deep Glacial Erosion, Kilometre Scale Folding, and the Start of the Snowdon Volcanic Group.
Looking south from the southernmost summit of the Carneddau Mountains (Pen yr Ole Wen, 3162ft/978m) to the sharp, steeply rising north ridge of Tryfan (3010ft/915m at left) and the deeply glacier scoured corries of the Glyder Mountains. The main Glyder Range summits of Glyder Fach, Glyder Fawr and Y Garn are arranged to its right across the centre foreground, and the distant, hazy peaks of Crib Goch, Snowdon (or Yr Wyddfa) and Garnedd Ugain peek over the Glyders on the right-hand skyline. The southern summits of the Carneddau Range, most of the Glyder Range, and Tryfan are formed by the steeply folded volcanic rocks and igneous intrusions of the Capel Curig Volcanic Formation, which are also interbedded with the shallow marine mudstones, siltstones and sandstones of the Cwm Eigiau Formation. These rocks are again part of the lower of the two final sequences of volcanic rocks (The Llewelyn Volcanic Group) that are preserved within the central part of the large down-fold of the Snowdon Syncline in northern Snowdonia. However, commencing with the so called ‘Pitts Head Tuff (which is a forerunner of, but sits just below) the second, and final major volcanic sequence, the Snowdon Volcanic Group now begins to appear, and can be seen here in the centre of the Snowdon Syncline, which runs towards us from the summit of Snowdon in the far distance. It then continues northwards, as part of the smaller Idwal Syncline (the broad valley to the left of Y Garn, the pyramidal summit in the middle distance, far right) scoops beneath the lake of Llyn Idwal (seen in shadow) and then runs northwards up the southern ridge of Pen yr Ole Wen towards the viewer. The up-folded eastern limb of the Idwal Syncline now forms the steeply dipping north ridge and west face of Tryfan (left) whilst the western limb rises up above Llyn Idwal to the summit of Y Garn. However, because of this folding, and later uplift, the main area of preservation of the Snowdon Volcanic Group is actually in the Snowdon Massif in the distance, which we will discuss in the next few pages.