Add PROFESSOR GEIKIE ON THE 
There can be little doubt that the Calciferous Sandstone series of the Forth 
basin is a mingled estuarine and marine equivalent of the Lower Limestone 
shale, and even perhaps of the lower parts of the Carboniferous Limestone 
of England. The fossils in the marine bands just referred to make this point — 
tolerably clear. But even the red sandstone group: below can be shown from 
evidence, elsewhere obtainable in Scotland, to be coeval with a Carboniferous 
Limestone fauna outside the present Scottish area. The abundant: fauna of 
the Carboniferous Limestone did not suddenly start into existence. It seems 
to have spread over the area of England before it had advanced into that of 
Scotland. It never, indeed, occupied the latter region so long, and so econ- 
tinuously, as it did the English and Irish tracts. Before it spread up towards 
the Highlands, it had been borne northward in excessive overflows of the sea, 
but did not succeed in establishing itself until the close of the Calciferous 
Sandstone series. At that time, a general subsidence of central Scotland 
appears to have taken place. A clear but shallow sea covered most of the 
ground between the chain of the Ochil and Lammermuir hills. At this 
epoch, the thick lower limestones were formed, which can now be traced 
continuously over so large an area. But that the sea did not obtain prolonged - 
possession of the area is shown by the intercalation of sandstones, shales, and _ 
coal-seams among the limestones, and by the thick mass of similar strata 
under which the limestones were buried. The coal-seams, with their root- 
charged under-clays, point to the submergence of many successive terrestrial, — 
or at least swampy surfaces, which had appeared over the site of the buried 
crinoid and coral limestones. | 
These changes of physical geography were accompanied in some places by 
abundant and continuous volcanic action. But the number of actual vents had 
decreased, Large tracts remained unvisited by any volcanic outbreak. Where 
the eruptions began most copiously they continued longest. Thus, in the south ; 
of Fife, they lingered on until the thick limestones and a considerable depth of 
been even more profusely poured out, they appeared intermittently, and on @ 
gradually waning scale, until after all the lower coals had been laid down. . 
action would appear to have ceased everywhere in the region of the Forth 
Basin, Not a trace of any interbedded volcanic rock has yet been met with in — 
the Millstone Grit or in the Coal-measures. So far as appears, therefore, the — 
outpouring of lava and ashes was entirely confined to the first half of the 
Carboniferous period. Nevertheless, the numerous intrusive masses of dolerite — 
which traverse even the uppermost parts of the Coal-measures show that | 
volcanic activity recommenced at some subsequent period. I shall be able | 
in the present memoir to adduce new evidence regarding the nature of these 
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