Proceedings of the lloyul Society. 397 



This part of the memoir was devoted exclusively to an attempt 

 to explain or account for the facta described in the first part of 

 the memoir. 



The geological epoch when the strata composing the coal-measures 

 of this district were deposited, was first noticed. It was stated 

 that these coal-measures were deposited at a period immediately 

 following the deposition of the old red sandstone formation ; and 

 that this older formation was to be seen both on the north and on 

 the south sides of the Lammermuir Hills, dipping under the coal- 

 measures, and resting on the upturned greywacke strata of these 

 hills. The lowest member of the old red sandstone group is a 

 coarse conglomerate, evidently formed by the denudation of these 

 greywacke hills ; and the uppermost members consist of soft argil- 

 laceous sandstone, of a deep red colour. 



The coal-measures of this particular district extend also over 

 the whole of East Lothian, though towards the north and north- 

 east, they are much broken and shattered by eruptions of trap. Be- 

 yond the east and south-east crop of the Tyne Coal Basin, there 

 are no members of the coal-measures proper, except those which 

 occupy the lowest part of the series. The limestone known in the 

 Esk and the Tyne Basins, as lying under the North Greens Coal, 

 undulates along or near the surface, throughout all the country be- 

 tween Haddington and the sea, towards North Berwick, as well as 

 Dunbar and Dunglass, except at those places now occupied by trap 

 hills. 



It appears that along the east margin of the Tyne B.isin there is 

 an anticlinal line, from which the limestone just spoken of dips 

 gently to the east, so as to form in some measure a third basin, but 

 one very flat and much broken. 



The author proceeded next to speculate on the probable mode 

 in which the strata of the coal-measures had been severally formed. 

 It was inferred from various circumstances, that they must have 

 been all deposited at the bottom of an aqueous medium, which in 

 certain parts, or at certain periods, was calm and tranquil, and which, 

 in other parts, or at other periods, was agitated by currents. 



The shales and clays, it was said, might have been formed of se- 

 diment washed down from the Lammermuir Hills ; but it was 

 thought that the siliceous sediment necessary for the enormous de- 

 posits of sandstone must have come, not from the greywacke hills 

 chiefly, but from primitive formations, and which were probably 

 situated far off^ towards the west and north. 



In regard to the origin of the limestone strata in the district, it 

 was inferred, that they had been formed by a precipitate of carbo- 

 nate of lime, held in solution by the aqueous medium which over- 

 spread the district. Water, it was said, would hold carbonate of 

 lime in solution, if there was an excess of carbonic acid ; and on 

 the application of heat, a part of the carbonic acid gas would be 

 liberated, and a precipitate occasioned. To account for the remark* 

 able fact, that the limestone underlying the North Greens coal 

 thickened as it approached the Lammermuir Hills, it was suggested 



VOL. XXV. NO. L. — OCTOBER 1838. D d 



