TAYLOE— TORBANE MINERAL EIELD. 



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 Binuy ; 

 sometimes in round circular nodules in the trap or limestones ; and 

 sometimes oozing out liquid from trappeau 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- 

 chanicall_7 mingled with it ; than that the sandstone was subsequently 

 saturated from beneath. 



Eacts 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. 



G-iven 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 



