CHAP. XIX 
ERUPTIONS IN ARRAN AND CANTYRE 
Eeference has already been made to the comparative scarcity of sills m 
this region, and to the occurrence of the acid group of Lintratheii porphyry 
and the more basic sheets behveeii the Firth of Tay and lorfar Ihis 
scarcity no doubt arises in part from the extent to which the rocks that 
underlie the volcanic series are concealed. Yet it is notevoithy that alon 
the coast-section of these rocks near Stonehaven hardly any intrusive sheets 
are to be seen. 
3. Tlic Arran and Cantyrc Centre 
It is unfortunate that the Ochil cliain should be broken across and 
buried under vounger formations at the very place where some ol the most 
interesting veiits in the whole area of the Old Fed Sandstone 
been looked for.' We have to pass westwards across the lirth ot Ll}de to 
the Isle of Arran before we again meet with rocks of the same age and 
""^'“irthe course of the recent work of the Geological Survej^ in that 
island, Mr. W. Gunn has discovered that the Lower Old Led Sandstone 
includes some interstratified volcanic rocks on the north side of Xoith G en 
Sannox, and he has supplied me with the following notes 
“ The area in which the volcanic intercalations occur is much faiilted and 
only a part of it has been maiiped in detail, but the position of the iiiter- 
Sded igneous rocks is quite clear. The Old Led Sandstone here consis s 
of three distinct members, the lowest of which is made up ot coarse, we 
rounded conglomerates, alternating with sandstones and purple mudstones^ 
Above this, and apparently uncoiiforniable to it, is a iniddle saies of lig 
coloured conglomerates and sandstones, the pebbles in which are maiiilj o 
(luartz Finally comes an upper series of red sandstones and coiiglomeiates, 
ihich occupy nearly the whole of the coast section and it is this senes which 
has generally been taken as the typical Old Led .Sandstone of the islai . 
The volcanic series is intercalated between tlie middle 
cdven above, and may be seen in several places on the hillside between the 
shepherd’s house at Nortli Sannox and Laggan. It consists mainly ot old 
lavLbeds of a dull reddish or purplish colour, often soft and m pl^ces much 
decomposed. It seems basic in character. A specimen from near the 
Fallen Locks, examined by Mr. Teall, was found to be too much altered toi 
precise determination, but was probably a basalt originally. These rocks do 
not occur on the cotxst. . r r.i 
I„ the smithern extremity of Coi.tyre tome unporte.t relies ot he 
voloairic rooks of the Lower Old lied Wstooe have been .mc»t j 
detected and nmpred tor the Geological bi.rvcy by SIi, h. G. hjmes. 
... , . ■ „nrtl.-easteni part of Lake Caledonia ; also to the oceurrenee of 
with the volcanic^ senes ^ crystalline schists near Loch Lomond (cente, p. 272). 
isolated masses of ireec “ P exiimple of the abrupt termination of a volcanic band near 
1 The Ochil area - - ,pydden disappearance of the rentland lavas and tufts 
Its centre owing ^ ^ another striking illustration. 
on the northern Side ot the is52 an account of the geology of the southern 
porUo^of CaiityreV He' gmiiped all the igneous rocks of the district as one series, which he 
