6o 
THE PERMIAN VOLCANOES 
BOOK VII 
Fig. 200. — Section of lavas 
east side of Mauchline Hill. 
tuff and volcanic breccia occur there, interleaved with seams of red sand- 
stone, like the chief mass of that rock, into which they gradually pass 
upward. Yet, even among the sandstones above the main body of tuff, 
occasional nests of volcanic lapilli, and even large 
bomb- like lumps of slag, point to intermittent ex- 
plosions before the volcanoes became finally extinct 
and were buried under the thick mass of red Permian 
sandstone. 
There is good reason to believe that both the 
volcanic sheets and the red sandstones overlying 
them, instead of being restricted to an area of only 
about 30 square miles, once stretched over the low- 
lands of Ayrshire ; and not only so, but that they 
ran down Nithsdale, and extended into several of 
its tributary valleys, if indeed, they were not con- 
tinuous across into the valley of the Annan. 1 Traces 
of the lavas and tuffs are to be found at intervals 
over the area here indicated. The most important 
display of them, next to their development in Ayrshire, occurs in the 
vale of the Nith at Thornhill, whence they extend continuously up the 
floor of the Carron Valley for six miles. They form here, as in Ayrshire, a 
hand at the base of the brick-red sandstones, and consist mainly of bedded 
lavas with the basic characters above referred to. These lavas, however, 
are followed here by a much thicker 
development of fragmental volcanic 
materials. Abundant volcanic de- 
tritus is diffused through the over- 
lying sandstones, sometimes as a 
gravelly intermixture, sometimes in 
large slaggy blocks or bombs, and 
sometimes in intercalated layers of 
tuff, while an occasional sheet of one 
of the dull red lavas may also be FlQ - 201 • — Section of the top of the volcaiiie series 
! , , , rp, n ^ ^ ■ „ near Eastside Cottage, Carron Water, Nithsdale. 
detected. The final dying -out of 
the volcanic energy in a series of intermittent explosions, while the ordinary 
red sandy sediment was accumulating, is here also admirably chronicled. 
As an illustration of these features the accompanying section is given 
(fig. 201). The last of the lavas (a) presents an uneven surface 
against which the various kinds of detritus have been laid down. First 
comes a coarse volcanic breccia (b) made up of angular and subangular 
blocks of different lavas imbedded in a matrix of red ashy sand. 
This deposit is succeeded by a band of dull red tufaceous sandstone, 
evidently formed of ordinary red sandy sediment, into which a quantity of 
volcanic dust and lapilli fell at the time of its accumulation. Some of the 
ejected blocks which lie inclosed in the finer sediment are upwards of a 
1 See Memoirs of Geol. Surv. Scotland, Sheet 15 (1871), p. 35 ; Sheet 9 (1877), p. 31. 
