CARBONIFEROUS VOLCANIC ROCKS OF THE FIRTH OF FORTH BASIN. 449 
The thickness of strata in a section through the most volcanic part of the 
heights south of Linlithgow is about 2200 feet. It will probably not be an over- 
estimate to place the proportion of lava and tuff in that section at 2000 feet. 
Besides the necks and associated portions of igneous matter, the Linlithgow 
district presents numerous examples of intrusive igneous rocks belonging to an 
epoch long posterior to that of the Carboniferous volcanoes. They occur in 
two ferms,—1st, As large sheets intruded into the Millstone Grit and Coal- 
measures; 2d, As dykes running in a general east and west direction through 
all the other rocks, aqueous and igneous, including even some of the large 
intrusive sheets. ‘The dykes form a portion of that vast series which traverses 
Scotland and the north of England, and, as I have elsewhere shown, may with 
probability be referred to the Miocene period. ‘They therefore do not belong 
to the subject of the present memoir. The intrusive sheets of later date than 
the Coal-measures are, as I have said, probably younger than any part of the 
Carboniferous system, if, indeed, some of them are not overflows from the 
Tertiary dykes. As they present, however, some interesting features bearing 
on the subterranean action of igneous matter, I shall include references to 
_ them in the sequel. 
4. Stirlingshire District.—A relation may be traced between this district and 
that of Linlithgowshire, somewhat similar to what has already been stated to 
subsist between the Edinburgh and East Lothian volcanic areas. The 
Stirlingshire ground embraces a small part of the eastern prolongation of 
the Campsie Fells, which like the Garlton Hills consist chiefly of various 
“ porphyrites” and tuffs of later date than the red sandstones at the base of the 
Carboniferous system. There can be little doubt that the two latter areas were 
contemporaneously the scene of the same conditions of volcanic activity. The 
distance between them is about forty-five miles. Yet, while from these two 
centres the same kind of volcanic rocks were being copiously ejected, in the 
intermediate volcanic district of West Lothian all the lavas were of basaltic 
types, while the tuffs presented the usual characters associated with these 
pyroxenic rocks. Not a single sheet or dyke of porphyrite has been met 
with in any part of that district, with the trifling exceptions at Calton Hill 
and Arthur Seat. 
The voleanic history of the Stirlingshire district is sharply divided off into 
two periods. First comes the great pile of lava and tuff of the Campsie 
Fells. These immediately to the north of Kilsyth are seen lying conformably 
upon the upper part of the red sandstone group of the Calciferous Sandstone 
series. But except at the bottom they seem to be nearly without inter- 
stratifications of sandstones or other ordinary sedimentary strata. Their lower 
portions consist of slagey porphyrite-lava and thick beds of fine-grained stratified 
tuff, with some bands of red, green, and grey clays, and cementstone, and a 
VOL. XXIX. PART I, DZ 
