248 Geikie— Permian Volcanos in Scotland. 



the volcanic rocks described in tliis paper and lying near the base of 

 these sandstones afford now the proof of actnal volcanic eruptions in 

 Britain during the continuance of the Permian period. 



I have spoken only of the Ayrshire basin, but evidence of the 

 contemporaneous intercalation of volcanic rocks is not less clear 

 among the Permian sandstones of Nithsdale. The felspathic trap 

 laid open in the railway cutting at Drumlanrig is identical in its 

 mineralogical characters and general aspect with the Ayrshire mela- 

 phyi-es. Its upper surface has the usual slaggy amygdaloidal cha- 

 racter of the higher part of a lava-flow, and it is covered with gently 

 inclined red sandstones containing a few beds of gravelly tuff or 

 breccia like that of Ballochmyle. In the Carron Water there are 

 some excellent sections of these rocks showing the red sandstones, 

 sometimes sprinkled with volcanic bombs and often interlaced with 

 bands of fine ash, angular tuff and even coarse volcanic breccia. 

 Along with these proofs of igneous action occur beds of vesicular and 

 amygdaloidal melaphyre, like those of the Ayr, and showing the 

 same radiating veins of horizontally stratified red sandstone which 

 fill up cracks in the original lava-form mass. The course of the 

 Can-on Water furnishes ample proof of the existence of contemj)ora- 

 neous volcanic rocks in the Permian series of the south of Scotland. 

 The same evidence may be traceable southwards towards Dumfries, 

 but I have not yet had an opportunity of examining that part of the 

 district. 



Throughout the Carboniferous tracts of the Lowland Valley of 

 Scotland there are many igneous rocks which must be later than 

 even the Upper Coal-measures, but of which the geological date can- 

 not be approximately fixed. Some of these rocks are comparable 

 with parts of the Ayrshire series, and it becomes an interesting 

 question whether they may not belong to the same period. The de- 

 termination of an actual date among the post Carboniferous igneous 

 rocks is one which may be of great use in working out the geologi- 

 cal history of the broad Lowland valley. And it is likewise not 

 without its interest, as it enables us to connect the British type 

 of the Permian system by another link with that of the centre of 

 Europe. 



It may be mentioned, in conclusion, that the Permian basins of the 

 south-west of Scotland are traversed by a set of intrusive doleritic 

 traps, sometimes as irregular bosses (/in Fig. 1), or as dykes and beds. 

 These rocks have no relation to the Permian volcanic group, further 

 than that they came through it as well as through the sandstones. The 

 dykes belong to that remarkable N.W. or N.N.W. series which runs 

 across Scotland and the north of England. I called attention to 

 these dykes some years ago,^ and suggested that they might be as 

 late as the Middle Oolite. Since that time additional evidence has 

 been accumulating, and I believe it will be possible to show good 

 groimds for believing that they are not only as late as the Oolitic 

 period, but may even be of Tertiary age. 



J [Trans. Eoy. Soc, Edin., sx, p. 650.] 



