Subsequently, in the Tertiary period, there were two enormous outpourings of volcanic material - first andesitic lava, and later, after a long interval of quiet, rhyolitic - which nearly half filled the basin, converted it into a plateau and broke up the mountain rim.
The lavas and ashes are for the most part andesitic.
They are often accompanied by volcanic rocks, which are mainly andesitic, and they commonly lie unconformably upon the older beds.
The lavas and ashes which form these cones are mostly andesitic. Mud " volcanoes " occur upon the Makran coast, but it is doubtful whether these are in any way connected with true volcanic agencies.
The axis along which they have been elevated runs north-east and south-west, and on either flank a series of " green rocks " appears, consisting of altered amygdaloidal andesitic lavas, intrusive dolerites, coarse gabbros and diorites, and at Beagh-beg and Creggan in central Tyrone ancient rhyolitic tuffs.
