Like many of the mountain ranges in County Kerry, such as the
MacGillycuddy Reeks, the mountains of the Central Dingle peninsula are composed predominantly of
Devonian period
Old Red Sandstone, with a band of
Ordovician period
metasediments. The rocks date from the Upper
Devonian period (310–450 million years ago) when Ireland was in a hot equatorial setting. During this 60 million year period, Ireland was the site of a major basin, known as the Munster basin, and Cork and Kerry were effectively a large alluvial floodplain. Chemical oxidation stained the material with a purple–reddish colour (and green in places from chlorination), still visible today. There are virtually no fossils in Old Red Sandstone. The composition of Old Red Sandstone is variable and includes
sandstones,
mudstones,
siltstones, and
conglomerates (boulders containing quartz pebbles are visible throughout the range). The mountains were subject to significant glaciation with
corries and
U-shaped valleys, however the range does not have the sharp rocky
arêtes and ridges of the MacGillycuddy Reeks range. ==List of peaks==