440 PROFESSOR GEIKIE ON THE 
author clearly recognises that many of the igneous rocks were thrown out con- 
temporaneously with the strata among which they occur. He constantly seeks 
for analogies among modern volcanic phenomena, and presents the igneous 
rocks of the Lothians not as so many petrographical varieties, but as monu- 
ments of different phases of volcanic action previous to the formation of the 
Coal-measures. His detailed descriptions refer chiefly to Arthur Seat and the 
Pentland Hills, to which alone the work was originally intended to refer. 
They may be cited as models of exact and luminous research. The portions 
referring to the rest of the basin of the Forth do not profess to be more than a 
mere sketch of the subject. 
The first chronological grouping of all the intercalated sheets of igneous 
rock in the region was that made by myself for the Geological Survey. The 
general order of succession of the strata was carefully worked out, and the 
horizon of each sheet of volcanic rock could thus be definitely fixed. In the 
memoirs illustrative of Sheets 32, 33, and 34 the general structure of the country 
from Linlithgow to Berwick-on-Tweed was traced, and the part taken by the 
igneous rocks was there described. 
Since the appearance of the maps and memoirs of the Survey, prolonged 
study of igneous rocks in other parts of Britain and abroad has given me 
further insight into the history of volcanic action in this district of 
Scotland. The application of microscopical examination has opened up a— 
new field of inquiry, giving new methods of mineralogical analysis and com- 
parison, and new aids in the investigation of ancient volcanic processes. I 
propose therefore, in the present memoir, to offer to the Society a general view _ 
of the volcanic phenomena associated with the Carboniferous rocks in the basin 
of the Forth, derived on the one hand from a study of the rocks in the field, 
and on the other from an examination and comparison of them under the 
microscope. ‘iQ 
The subject thus divides itself naturally into two parts,—I1st, The larger 
relations of the rocks to each other and to the associated stratified formations, 
including the geological structure of the masses, their chronology and the 
succession of events of which they are memorials; 2d, The minute and 
internal composition and relations of the rocks, chiefly as revealed by the 
microscope. The former subdivision may be termed Stratigraphical, the 
second Petrographical. 
