CHAP. XXXI 
AYRSHIRE , NITHSDALE AND ANNANDALE 
61 
foot in length. A more vigorous discharge of fragmental material is shown 
by the next bed (d), which consists of a coarse nodular tuff, mingled with a 
little red sandstone and crowded witli blocks of the usual lavas. Beyond 
the locality of this section these tuffs are found to pass up insensibly into 
the ordinary Permian sandstone. 
But we can detect the edges of yet more distant streams of lava emerg- 
ing from under the red sandstones and breccias to the east of the Nitli. 
On the farther side of the Silurian ridge that forms the eastern boundary 
of the Nitli valley, above which it rises some 700 or 800 feet, there is 
preserved at the bottom of the valley of the Oapel Water, which flows into 
Annan dale, another small outlier of a similar volcanic band, three miles 
to the south-east of it two little fragments of the volcanic group lie on the 
sides of a small tributary of the Water of Ae. Since these may serve as a 
good illustration of the extent to which denudation has reduced the area 
of the Permian volcanic series, a section of the locality is here given (Fig. 
202). The general foundation rocks of the country are the Silurian grey- 
wackes and shales in highly inclined and contorted positions (a). Each 
outlier has, as its basement material, a volcanic breccia (bb) in which, together 
with the usual lava-fragments, are mingled pieces of the surrounding Silurian 
strata. In the smaller outlier lying to the north-east, this detrital layer 
is only about one foot thick. It is overlain by a slaggy amygdaloid of the 
usual character (cc), which in the lower outlier is covered with boulder clay 
(d). There can be little doubt that these detached fragments were once 
united in a continuous sheet of lava which filled the valley of the Water of 
Ae and that of its tributary. That the lava stretched down the Ae valley 
for some distance is proved by the occurrence of another outlier of it two 
miles below. 
But there is still additional evidence for the wide extension of these 
volcanic sheets. It appears to be certain that they stretch far to the east- 
ward, under the Permian sandstones of the Lochmaben basin of Annandale, 
for breccias largely made up of pieces of the bedded lavas are found close to 
the northern edge of the basin on the west side of the hiver Annan. To this 
remarkable adherence of the lavas and tuffs to the bottom of the Permian 
valleys I shall afterwards more specially refer. 
The thickness of the whole volcanic group cannot be very accurately 
determined. It reaches a maximum in the Ayrshire basin, where, at its 
greatest, it probably does not exceed 500 feet, but is generally much less; 
