78 
THE PERMIAN VOLCANOES 
BOOK VII 
again between Elie ancl St. Monans, it may be noticed that the mass of 
material adhering to the wall of a neck, exposed in ground-plan upon the 
beach, 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, laid bare on the present shore, 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 recognizable 
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 some of the Fife vents, indeed, the fragments of 
shale, sandstone and other sedimentary strata are so unchanged that they 
cannot on a fresh fracture be distinguished from the adjacent parent strata. 
The Spiri/ers, Lingulm, 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 in situ. 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 ol alteration has depended not merely upon the heat of the 
volcanic vent, but also in great measure upon the susceptibility of the frag- 
ments to undergo change and the duration of their exposure to it. 
Dr. Heddle has computed the temperature to which fragments of shale, 
etc., in tuff-necks of the Fife coast have been subjected. He found that the 
bituminous shales have lost all their illuminants, and of organic matter have 
retained only some black carbonaceous particles ; that the encrinal lime- 
stones have become granular and crystalline ; that the sandstones present 
themselves as quartzite, and that black carbonaceous clays show every stage 
of a passage into Lydian-stone. He inferred from the slight depth to which 
the alteration has penetrated the larger calcareous fragments, that the heat 
to which they were 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. 1 
It may be perhaps legitimate to infer that, while the fragments that 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 hand, which were discharged by the aeriform explosions from the cool 
upper crust, on the first outburst of a vent, would not exhibit any trace of 
such a change. Where, therefore, we meet with a neck full of fragments of 
unaltered stratified rocks, we may suppose it to have been that of a short- 
lived volcano ; where, on the other hand, the fragments are few and much 
altered, they may mark the site of a vent which continued longer active. 
1 Trans. Roy. Soc. Edin. vol. xxviii. p. 487. 
