CARBONIFEROUS VOLCANIC ROCKS OF THE FIRTH OF FORTH BASIN. 459 
east of Fife such traces may frequently be found here and there on the outside 
of the vents. At Largo, and again between Elie and St Monans, I have 
observed that in the ground-plan exposed upon the shore the mass of material 
adhering to the wall of a neck often consists largely or even wholly of debris of 
sandstone, shale, and limestone, while the central and chief mass is made up 
of green tuff or agglomerate, with occasional pieces of the surrounding stratified 
rocks scattered through it. It seems probable, therefore, that the sections of 
these Fife necks, now exposed by the present beach, do not lie far below the 
original crater-bottoms. 
Some light might be expected to be thrown upon the phenomena in an 
active volcanic chimney by the condition of the fragments of recognisable 
sedimentary rocks imbedded in the ejected debris which has filled up the 
orifice. But the assistance from this source is neither so full nor so reliable as 
could be wished. In a great many cases indeed the fragments of shale, sand- 
stone, and other sedimentary strata are so unchanged that they cannot on a 
fresh fracture be distinguished from the parent beds at a short distance from 
the vent. The spirifers, lingule, crinoids, cyprid-cases, ganoid scales, and 
other fossils, are often as fresh and perfect in the fragments of rock imbedded 
in tuff as they are in the rock 7m stu. In some cases, however, distinct, and 
occasionally even extreme, metamorphism may be detected, varying in intensity 
from mere induration to the production of a crystalline texture. The amount 
of alteration has depended not merely upon the heat of the volcanic vent, but 
also in great measure upon the susceptibility of the fragments to undergo 
change. 
My friend Dr HEppDLE endeavoured to estimate the temperature to which frag- 
ments of shale, &c., in tuff-necks of the Fife coast had been subjected. He found 
that the bituminous shales had lost all their illuminants, and of organic matter 
had retained only some black carbonaceous particles ; that the encrinal lime- 
stones had become granular and crystalline ; that the sandstones presented 
themselves as quartzite, and that black carbonaceous clays showed every stage 
of a passage into Lydian-stone. He inferred from the slight depth to which 
the alteration had penetrated the larger calcareous fragments, that the heat to 
which they had been exposed must have been but of short continuance. As 
the result of his experiments, he concluded that the temperature at which the 
fragments were finally ejected from the volcanic vents probably lay between 
660° and 900° Fahr.* 
It may be perhaps legitimate to infer that while the fragments which fell 
back into the volcanic funnel, or which were detached from the sides of the 
vent, after having been exposed for some time to intense heat under con- 
siderable pressure, would suffer more or less metamorphism, those on the other 
* “Trans. Roy. Soc. Edin.” xxviii. p. 487. 
