186 Reports & Proceedings — Edinhiirgh Geological Society. 



ISth January, 1922.— Mr. T. Cuthbert Day, F.C.S., F.E.S.E., 

 President, in the chair. 



1. " A Basalt Laccolite at Bo'ness." 



2. " The Edge of a Carboniferous Volcano." 



3. Exhibit of Specimens showing Contact Alteration of Coal, etc. 

 By H. M. Cadell, B.Sc, F.E.S.E. 



Mr. Cadell described a basalt laccolite in the Bo'ness Coalfield that 

 had recently been proved in numerous borings to the Smithy Coal 

 seam. Under a large part of the Bo'ness Coalfield there had long 

 been known to exist a harmless bed of whinstone between the Main 

 and the Smithy Seams, which differed from the inter-bedded basalt 

 lavas of the district in being intrusive. At Bridgeness this rock, 

 which was usually about 20 feet thick, suddenly changed its position 

 and swelled into a lenticular mass that reached a thickness of 106 

 feet at one place, and formed a small laccolite such as had been 

 found on a much larger scale in other countries. The effect of the- 

 intrusion was to destroy the coal within 10 feet of it, but the coal 

 was not rendered anthracitic as it was converted into a hard 

 carbonaceous mass full of calcite and chalybite veins of no economic 

 value. 



One interesting fact had been proved, viz. that the whinstone 

 had been forced like a wedge between the strata without melting 

 or absorbing any part of the surrounding rock. In one bore the 

 whinstone had split the Smithy coal into two parts, and the upper 

 half of the seam was separated from the lower part by a solid sheet 

 of basalt 97 feet thick. A quarter of a mile away the unwelcome 

 invader had shrunk to a sill only 4| feet thick, and the coal was 

 quite good only a few feet from it. The course of the sill was very 

 erratic, and there were places where it did not occur at all, and much 

 boring was required to ascertain exactly the amount of coal that was 

 destroyed. 



Specimens of the burnt coal and the basalt were exhibited. 



Mr. Cadell next dealt with other volcanic phenomena of the 

 Carboniferous Limestone jjeriod in West Lothian. The first 

 eruptions at the close of the Oil Shale period were of ash, and later 

 a great volcano situated to the west of Linlithgowshire poured out 

 floods of lava which overwhelmed the forests and became inter- 

 bedded among the coal-bearing strata as they were being deposited. 

 Some deep bores had been made in search of coal to the west and 

 south of Bo'ness, and, instead of finding useful minerals, had pierced 

 nothing but lavas and ash beds more than 1,400 feet thick without 

 getting through the volcanic pile. The Bo'ness Coalfield was on the 

 edge of a large volcanic island that existed to the west, and on this 

 great heap of lavas and ash beds the coal forests did not exist, or 

 at least produce coal seams until the volcano became extinct after 

 the Index Limestone was formed. A section was shown of the 

 edge of this volcano as disclosed by bores and pits sunk through 

 the volcanic rocks in that quarter. 



