334 
VOLCAiVOES OF THE LOWER OLD RED SANDSTONE kook v 
From the arrangement of the veins of sandstone it is evident that 
irregularly divergent, but often more or less stellate, fissures opened in the 
lavas as they cooled. Sometimes, indeed, the molten rock appears to have 
broken up into a shattered mass of fragments, as must often have happened 
when lavas were poured over the lake-floor. What may be an instance of this 
effect is to be seen on the cliff under the 
walls of Turiiberry Castle, whence the 
annexed sketch (Fig. 96) was taken. 
Tlie lower andesite (a) is highly amygda- 
loidal towards the top, and is traversed 
Q>-cPA'<=^Q 
in all directions with irregular veins and 
nests of sandstone which can be traced 
upward to the bed {h), consisting of sand- 
stone, but so full of lumps or slags of 
amygdaloidal andesite that one is here 
and there puzzled whether to regard it 
as a sedimentary deposit, or as tlie upper 
layer of clinkers of a lava-stream strewn 
with sand. Above this fragmentary layer 
lies another bed of andesite (c) of a 
coarsely amygdaloidal structure, which 
encloses patches of the underlying sand- 
stone. It passes upward, in a space of 
from four to six feet, into a mass of 
angular scoria ceous fragments (d) of all 
sizes up to blocks 18 inches in length 
cemented in a vein-stuff of calcite, chalce- 
dony and quartz. This brecciated structure ascends for about 13 or 14 
feet, and is then succeeded by a greenish compact andesite (e), which further 
north becomes amygdaloidal and much veined with sandstone, passing into 
a breccia of lava fragments and sandstone. 
The remarkable brecciated band (d) in this cliff, though 13 or 14 feet 
FiO. 96. — Section of andesites, Tui-nberry 
Castk', Ayrsliire. 
Fig. 97. — Lenticular form of a brecciated andesite (shown in Fig. 96), Tuniberry, Ayrshire. 
in the centre, immediately thins out on either side, until in the course of a 
few' yards it completely disappears and allows the lavas c and e to come 
together, as shown in Fig. 97. We may suppose that this section reveals 
