TAYLOR — TORBAITE MINERAL FIELD. 
45 
be only explicable on the hypothesis that they were emptied at the 
same time that the other strata were deposited. 
The chemical changes effected by these igneous strata on the sur- 
rounding rocks are likewise very curious. In many places the lime- 
stone is changed into a crystalline marble. One bed at Kirkton 
affords undoubted evidence that it was deposited by a thermal spring. 
The great thickness the main bed of limestone in the hills attains, 
may be accounted for as much from its being a chemical deposit, as 
one of animal origin. The sandstones and shales, too, are often curi- 
ously baked, showing the violence of the igneous agencies. But we call 
special attention to the prevalence of bitumen in the district, some- 
times appearing solid in the crevices of the sandstones, as at Binny ; 
sometimes in round circular nodules in the trap or limestones ; and 
sometimes oozing out liquid from trappean reservoirs. 
The circular type of structure is very prevalent in the aqueous 
rocks of the district, as in the sandstone at King's Cavel, and 
amongst the ironstones. It extends throughout the rock sys- 
tems. It is most manifest in the oolite or roe-stone of another for- 
mation. However we may explain it, it is clearly the result of agen- 
cies at work when the sandstones and shales were depositing, and 
not a subsequent chemical change- This admitted, it follows that 
most of the bitumen of the district is contemporaneous with the 
igneous rocks, and that the highly bituminous sandstones and shales 
were saturated at the period of their deposition. The clearest proof 
of this is the structure of the celebrated Binny sandstone. How 
else can we explain the black bituminous patches appearing on its 
surface ? The physical agency at work may have been the conjunction 
of two rapid currents. But it is much easier to suppose the bitumen 
ejected from some neighbouring volcano floated in the waters of the 
lagoon or river in which the sandstone was forming, and then me- 
chanically mingled with it ; than that the sandstone was subsequently 
saturated from beneath. 
Tacts connected with the occurrence and formation of bitumen at 
the present day bear out this hypothesis. Its connection with volcanic 
agency is well known. The celebrated pitch-lake of Trinidad stands 
in close proximity to a volcano, as also do some of the bituminous 
localities in Asia Minor. All the three varieties of this substance 
float on water. Maltha, or mineral pitch, floats on the surface of the 
Dead Sea. Petroleum floats on the Tigris and Euphrates, so much 
so, that the surface of the river is often set on fire. The boatmen on 
the Tigris and Euphrates are paid in this substance. Doubtless at 
the bottom of these rivers there are many nascent beds of richly bitu- 
minous shales. 
Griven then a series of submarine volcanos ejecting out sheets of 
liquid bitumen, and at the same time sand and mud rapidly deposited ; 
let these commingle, and we have the rationale of the formation of 
the Binny sandstone, and the bituminous shales of Queensferry and 
Broxburn. These forces ceased after a time. A morass was slowly 
formed which now constitutes the Houston coal-bed. This indicates 
