332 
SILURIA. 
[Chap. XIII. 
part of the Isle of Arran which Sedgwick and myself classed as New Red Sand- 
stone at a period when the Permian classification was unknown. Recently 
Mr. Geikie has ascertained that subordinate to the lowest zone of the Permian 
rocks of Ayrshire there are beds of cotemporaneous igneous rock, — a point of 
exceeding interest in showing that in parts of Britain, as throughout Central 
Germany, volcanic evolutions were frequent in the period of the Lower 
Permian. 
Professor Harkness and myself have also expressed the opinion that the va- 
luable hematite which often occurs in a breccia at the base of the Permian rocks 
of Cumberland was formed at the commencement of this era, so marked by the 
great changes which occurred after the Carboniferous era. This observation is 
one of great interest j for it demonstrates that in our own country there exist 
the same evidences of igneous activity in this epoch, particularly in its earlier 
part, which are so common in the Roth-liegende or Lower Permian of Germany. 
The accompanying woodcut, drawn by Mr. Geikie, explains the phenomena which 
occur in Ayrshire, where submarine volcanic action has manifestly occurred 
during the accumulation of the Permian rocks, all the deposits having long after- 
wards been penetrated and traversed by eruptive greenstones : — 
Section across the Permian Basin of Ayrshire. 
N.W. S.E. 
Balloch- 
Little Hill. Mossgiel. Mauchline. myle. Catrine. Scorn-hill. 
ad a b c e b c f a da 
f. Intrusive greenstone (dolerite) coming through the Permian trap-rocks, e. Brick- 
red sandstones, d. ' Necks ' of Volcanic agglomerate, of Permian age. c. Beds of fel- 
spathic amygdaloidal trap with interbedded brick-red Permian sandstones, b. Trap-tuff 
and brick-red ashy sandstone of Permian age. a. Upper Carboniferous sandstones 
and shales. 
u The brick-red Permian sandstones of the Ayr (e) occur in a basin about six 
miles long and four or five miles broad. This basin is completely encircled with 
a ring of igneous rocks (6, c), which lie upon the upper red part of the Coal- 
measures (a) and form the base of the Permian series. They consist of dark- 
brown, purple, or chocolate-coloured porphyries or melaphyres, often highly 
slaggy and amygdaloidal, and of coarse volcanic agglomerate, and fine gravelly 
tuff, mingled with the ordinary red sediment of the Permian sandstones. That 
these volcanic rocks belong to the Permian series is shown by the fact that (con- 
taining beds of the usual sandstone of that series, which differs conspicuously 
from the red sandstones of the underlying Coal-measures) they are regularly 
interstratified with the base of the Permian group. Around the outside of the 
volcanic ring occur numerous round hills and hillocks of coarse volcanic agglo- 
merate (d). These are true ' necks,' which descend vertically through the Coal- 
measures, altering the coal-seams. They are some of the orifices from which 
the melaphyres and tuffs were ejected. Igneous rocks of similar character occur 
in the Permian basin of the Nith, north of Thornhill, and probably in other 
parts of that basin *. It may, in the end, be ascertained also that many of the 
igneous masses which perforate the Carboniferous rocks along the wide central 
valley of Scotland are likewise of Permian age." 
* See ' Geological Magazine ' for June 18(56. 
