1887.] Professor Geikie on Geology of St AWs Head. 177 
6. Geology and Petrology of St Abb’s Head. By 
Professor J. Geikie. (Plate VI.) 
I. Introduction. 
The observations recorded in this paper have reference chiefly to 
the coast-sections at St Abb’s Head and Coldingham Shore. The 
district was geologically surveyed some twenty-five years ago by 
my brother, Dr A. Geikie, and subsequently described by him in 
the Memoirs of the Geological Survey.* Since the publication of 
that memoir, no further examination of the ground in question 
appears to have been made. During the past summer I visited the 
neighbourhood, principally for the purpose of studying the igneous 
rocks which are so well exposed in sea-coast sections. At the date 
of the Government Survey of Eastern Berwickshire the aid of the 
microscope had not yet been invoked by field-geologists for the 
purpose of determining rock-species, and I was therefore curious to 
compare the igneous rocks of that region with those of similar age 
which I had studied elsewhere in Scotland, and more especially 
with the bedded and intrusive porphyrites and tuffs of the Gheviot 
Hills and the Sidlaws. 
The rocks of the district under review belong, as my brother has 
shown, to two great systems — the Silurian and the Old Ked Sand- 
stone. From Pettico Wick Harbour in the north, to Coldingham 
Bay in the south, the coast cliffs are composed almost exclusively 
of rocks of Old Red Sandstone age — Silurian strata appearing only 
for a short interval, a little to the north of Coldingham Shore. The 
latter reappear on the south side of Coldingham Bay, and continue 
along the shore to Callercove Point, in the neighbourhood of Eye- 
mouth. Inland from St Abb’s Head and Coldingham Shore they 
extend for many miles. (See Map, Plate VI.) 
II. The Silurian Rocks. 
To the description of the Silurian strata given in the Geological 
Survey’s Memoir, I have very little to add. They consist chiefly 
of greywackes and shales, generally inclined at high angles, and 
arranged in a series of more or less sharp anticlinal and synclinal 
folds, which have an average N.E. and S.W. trend. In their least 
* Geological Survey Memoirs : The Geology of East Berwickshire. 
VOL. xiv. 7/10/87 M 
