Proceedings of the Royal Society of Edinburgh. 385 



fiuviatile origin ; and the fact frequently observed, of these beds 

 feeing covered by, or alternating with, others containing only marine 

 remains, may, with great probability, be referred to changes in the 

 relative level of the land and sea that may have taken place while 

 these deposits were forming. 



The author then proceeded to describe the limits within which the 

 coal appears to have been deposited in the Scottish Lowlands, which, 

 with the exceptions pointed out by him, may, according to Williams, 

 be indicated by a line drawn from the mouth of the Tay passing 

 through Stirling, to the northern extremity of Arran ; and another 

 nearly parallel to it from St Abb's Head on the east coast, to Girvan 

 on the west. Although coal may not have been equally distributed 

 in every part of this district, — the deposition of the vegetable matter 

 from which it was derived, having probably been more or less in- 

 fluenced by local circumstances, which may also have caused occa- 

 sional varieties in the mineral structure and organic contents of the 

 associated strata, — yet, in the opinion of the author, there are suffi- 

 cient grounds to justify the conclusion, that the whole series origi- 

 nally constituted one great formation, the strata of which it is com- 

 posed appearing to have been deposited continuously, more or less, in 

 a horizontal position at the bottom of the sea, that must then have 

 covered at least the whole of that portion of the Lowlands, forming 

 either a strait or channel between two islands, or perhaps a vast es- 

 tuary in which the rivers of the neighbouring primeval countries dis- 

 charged their waters. The ripple-marks observable on the surface 

 of most of these beds give much additional probability to this suppo- 

 sition. 



This original continuity of the beds occupying the carboniferous 

 district, appears to have been subsequently interrupted by the intru- 

 sion of the igneous rocks and hills so universally prevalent in that 

 formation, by which they have been separated into the fields or basins 

 where they are now found. The effects of Plutonic action, by which 

 these hills were produced, seem to have been the chief agents em- 

 ployed in modifying the external surface of this important district, 

 and occasioning those chemical changes and combinations in the in- 

 terior of the earth, by which, when elevated above the waters, it was 

 •destined to become a more suitable habitation for the human race. 



The Pentland, Campsie, and Ochil hills, as well as many others 

 of a similar description within the limits specified, afford striking ex- 

 amples of the effects produced by their intrusion among the coal 

 strata, at periods subsequent to the consolidation of the latter, of 

 which some instances were noticed by the author. In fact, the 

 whole country occupied by the Scottish coal-measures, displays more 

 or less the influence of such igneous hills, or of the dykes connected 

 with them. A certain degree of parallelism may be traced between 

 the principal ranges, their general bearing being from the eastward of 

 north to the westward of south, which corresponds with the general 

 strike of the fossiliferous strata ; but they often appear to have been 

 protruded through the surface without any order or regularity, and 

 the dikes are found to proceed in every direction from the principa? 

 masses. 



