CHAP. XXI 
BERWICKSHIRE ERUPTIONS 
339 
regard the area as independent of any vents which may have risen farther 
west about Cockburn Law and the Dirrington Laws. Unfortnnately, how- 
ever, only a small part of the area comes into view, tlie rest of it lying 
heneatli the waters of the North Sea.^ 
Of the several vents dissected along this coast-line, one may he seen at 
Eyemouth, filled with a very coarse tumultuous agglomerate of andesite 
fragments embedded in a compact felspathic matrix, through winch are 
scattered broken crj'stals of felspar, and imperfect tabular crystals of black 
mica. Another of similar character is exposed for more than a mile and a 
half along the shore at Coldingham. It contains blocks, sometimes more 
than a yard in dhuneter, of different varieties of andesite, and, as at Eye- 
mouth, is much invaded by veins and bosses of intrusive andesite. 
To the nortli of Coldingliam, a series of liedded volcanic rocks which 
form the pieturescxue headland of St. Abb’s Head, are, according to the 
estimate of Professor James Geikie, about 1000 to 1200 feet thick, but 
neither their bottom nor their top is seen. The .same observer found them 
to consist of three groups of andesite sheets .separated and overlain by 
Fki. 98. — Section across tlic volcanic area otSt. Abb’s Hea.l (after Prof. J. Geikic). 
11 . Silurian formations ; 2. Lower Old Ked Conglomenite aud Sandstone ; 3 3. Slieets of andesitic lava ; 4. Volcanic 
tuffs, largely comixised of scoriifc in the biglier parts ; 5. Volcanic agglomerate of neck on shore ; C. Intrusive 
andesites, f, Fault. 
bedded tuffs. Tlte lowest lavas have their base concealed niider the sea, 
and are covered by a thick band of coarse agglomeratic tuff, above which 
lies the second group of andesites, about 250 feet thick. An intercalation 
of various tuffs from 40 to 50 feet thick then succeeds, followed by the 
third lava-group, 250 or 300 feet in depth. The highest member of the 
series is a mass of bedded tuffs some 400 feet thick. 
The andesites lie in beds varying from about 15 to about 50 feet or 
more in thickness. They are fine-grained, purplish-blue, or greyisli-blue, 
often reddish rocks, of the usual type. Generally rather close-grained, they 
are not as a rule very porphyritic, but often highly seoriaceous and amyg- 
daloidal, especially towards the top and bottom of each bed. The more 
slaggy portions are sometimes so filled in with fine tuff that the rock might 
be mistaken for one of fragmental origin. 
The bedded tuffs are usually well stratified deposits. Tlie most import- 
1 This area lie.s in Sheet 34 Geological Survey of Scotland, and was described by myself in the 
Memoir to accompany that Sheet (“Geology of Eastern Berwickshire,” 1864, p. 20). More 
recently the shoi’e between St. Abb’s Head and Coldingham has been remapped by Professor 
.Tames Geikie who has also studied the inicroscoiho character of the rocks, Froc. Moy. Soc. Rdin. 
xiv. (1887). 
