CHAP. XX 
A YRSHIRE ERUPTIONS 
333 
there after a considerable portion of the Lower Old Eed Sandstone had been 
deposited. These earlier strata were upraised, and on tlieir denuded ends 
another group of sandstones and conglomerates was laid down, followed by 
an extensive eruption of volcanic materials. 
It is the upper unconformable series that requires to be considered here, 
as it includes all the volcanic rocks of the Old Eed Sandstone lying to the 
west of the meridian of Dalmellington. The position of these rocks on 
their underlying conglomerates is admirably exposed among the hills between 
the valleys of the Boon and the Girvnn, as well as on Ecnnan Hill to the 
south of Straiton. The andesites rise in a craggy escarpment crowning long- 
green slopes that more or less conceal the conglomerates and sandstones below. 
Along the coast -sections the structure of the \-olcanic rocks may be 
most advantageously studied. The shore from the Heads of Ayr to 
Culzeau Castle affords a fine series of exposures, where every feature in the 
succession of the lavas may be observed. Still more instructive, perhaps, 
is the mile and a half of beach between Turnberry Bay and Houglaston, of 
which I shall here give a condensed account, for comparison with the coast- 
sections of Ivincardineshire and Forfarshire already described. 
The special feature of this part of the Ayrshire coast-line is the number 
of distinct andesite sheets which can be discriminated by means of the thin 
layers of sandstone and sandy tuff tliat intervene between them. In the 
short space of a mile and a half somewhere about thirty sheets can be 
recognized, each marking a separate outflow of lava. It was in this section 
that I first oliserved the sandstone-veinings which have been described in 
previous pages, and nowhere are they more clearly developed. Almost every 
successive stream of andesite has been more or less fissured in cooling, and its 
rents and irregular cavernous hollows have been filled with fine sand silted 
in from above. The connection may often be observed between these sand- 
stone partitions or patches aiul the bed of the same material, wdiich 
overspread the surface of the lava at the time that the fissures were lieing 
filled up. 
The andesites of the Turnberry shore are of the usual dark purplish-red 
to green colours, more or less 
compact in the centre and 
vesicular towards the top and 
bottom. They display with 
great clearness the large empty 
spaces that were apt to be 
formed in such viscous slaggy 
lavas as they moved along the 
lake - bottom. These spaces, 
afterwards filled with fine sand, 
now appear as irregular en- 
closures of hard green sand- 
stone embedded in the andesite. The example shown in Fig. 95 may be 
seen in one of the lavas at John o’ Groat’s Port. 
Fui. 95. — Cavernous spaces iu andesite, tilled in with sand- 
stone, John o’ Groat’s Port, Turnberry, Ayrshire. 
