196 
THE SILURIAN VOLCANOES 
BOOK IV 
part of Ayrshire which has been already cited as displaying so large a 
development of the volcanic series. Here the coast -sections reveal the 
intercalation of fossiliferons bands which show the true stratigraphical 
horizons of the lavas and tuffs. Under Bennane Head, Professor Lapworth 
some years ago found, in certain hardened black shales, a group of graptolites 
which mark an undoubted Arenig platform.^ Eecently the ground has 
been carefully re-examined by Messrs Peach and Horne, who have detected a 
number of other fossiliferons zones which confirm and extend previous 
observations. They have also been able to unravel the complicated 
structure of the volcanic series, and to represent it on the 6 -inch maps of 
the Geological Survey, of which a reduction on the scale of 1 inch to a 
mile is now in course of preparation. The following tabular summary, 
taken partly from notes made by myself during a series of traverses of the 
ground with Mr. Peach when the revision was begun, and partly from 
memoranda supplied by that geologist himself, may suffice as a general 
outline of the volcanic history of this exceedingly interesting and important 
region. 
Pentamerus grit. 
Conglomerate (Mulloch Hill). 
ts 
a 
'Shales, sandstones, grits, etc. (Ardmillan, Ealcletchie). 
Thick conglomerate (Byne Hill, Bennane, etc.). 
Thick fossiliferons limestone (Stinchar, Girvan). (On this horizon come 
the perlitio I'elsites and soda-felsites of Winkstone and Wrae.) 
Sandstone {Urthis confinis) passing down into thick conglomerate. 
o ■ 
CU m 
o 
§ 
c a 
[Unconformability.] 
Green mudstones, grits and greywackes. 
'Thin hand of dark mudstone with Upper Llandeilo graptolites, 
f Group of Eadiolarian cherts (about 70 feet) with alternating tufl's. 
I Tuff or volcanic conglomerate, with occasional lava-flows. 
I Black shale (10 feet) with Arenig graptolites. 
Volcanic breccias around local centres (Knockdolian, etc.). 
Thick group of porphyrite and diabase lavas. 
Bed flinty mudstones with Arenig graptolites. 
Porphyrites, etc. 
Fine tufl's, etc., with Lower Arenig fossils. 
^Diabase lavas, etc. (base not seen). 
It will be noticed from tliis table that the bottom of the volcanic series is 
not reached, so that no estimate can be formed of its full thickness, nor 
on what geological platform it begins. Possibly its visible portions repre- 
sent merely the closing scenes of a long volcanic history, which, over the 
area of the south of Scotland, extended into Cambrian time, like the contem- 
poraiy series of Cader Idris. 
Among the lowest lavas there are interstratified courses of fine tuffs, 
1 Oeol. Mag. 1889, p. 22. 
