152 PROCEEDIN^GS OF THE GEOLOGICAL SOCIETr. 



and volcanic breccia occur there, interleaved with seams of ordinary 

 red sandstone, 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 explosions 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 all the low- 

 lands of Ayrshire ; and not only so, but ran down JS'ithsdale, and 

 extended into several of its tributary valleys, if, indeed, they were 

 not continuous across into the valley of the Annan.-^ Traces of 

 the lavas and tuffs are to be found at intervals over much of the 

 area here indicated. The most important display of them, next 

 to their development in Ayrshire, occurs in the vale of the With at 

 Thomhill, whence they extend continuously up the floor of the 

 Carron Yalley for six miles. They form here, as in Ayrshire, a 

 band 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 detritus is dif- 

 fused through the overlying sandstones, sometimes as a gravelly 

 intermixture, sometimes in large slaggy blocks or bombs, and some- 

 times in intercalated layers of tuff, while an occasional sheet of one 

 of the dull red lavas may also be detected. The final dying-out of 

 the volcanic energy by a series of intermittent explosions, while 

 the ordinary red sandy sediment was accumulating, is here also 

 admirably chronicled. 



But we can detect the edges of yet more distant streams of lava 

 emerging from under the red sandstones and breccias to the east of 

 the Nith. On the farther side of the Silurian ridge, which forms 

 the eastern boundary of the Nith Yalley, above which it rises some 

 700 or 800 feet, there is preserved at the bottom of the valley of 

 the Capel Water, which fiows into Annandale, 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, while another outlier may be ob- 

 served two miles lower down the latter stream. But we have evi- 

 dence that the volcanic materials extend still farther eastward under 



1 See Memoirs of Geol. Surv. Scotland, Sheet 15 (1871), p. 35 ; Sheet 9 

 (1877). p. 31. 



