MR MILNE ON THE MID-LOTHIAN AND EAST-LOTHIAN COAL-FIELDS. 



261 



in this computation, consist chiefly of argillaceous matter ; — so that in a north 

 and south direction, the argillaceous rocks ai-e more equally distributed over the 

 district than the arenaceous rocks. 



In an east and west direction, the shales and clays, like the sandstones, are 

 much thicker on the west side of the basin, than on the east. 



(6.) There is one other inference which an examination of the above tables 

 warrants us in drawing, and it is one of some importance, in reference to the 

 history and formation of these several classes of rocks. That class in which the 

 greatest and most sudden variations of thickness occur, is the arenaceous class : 

 the class 'in which these variations are the least, are the carbonaceous; whilst 

 the argillaceous and the calcareous hold in this respect, a middle place. 



In illustration and proof of this remai-k, that it is in the arenaceous or sand- 

 stone strata, that the greatest variations of thickness in the same bed occur, a 

 few cases may be here given. 



In the workings at Preston (one-half mile east of Prestonpans) there is the 

 following section ; A is a stratum of fire-clay generally 4^ feet thick, B is a stra- 



tum of sandstone generally 4^ feet thick, C is a seam of coal. At one place the 

 sandstone thins away to nothing, and the fire-clay thickens, so as to fill up the 

 hollow in the sandstone, and to come in contact with the coal. It is there be- 

 tween 8 and 9 feet thick. 



The next example I shall mention of a sudden thickening of sandstone is 

 stiU more remarkable. At New CraighaU there are two seams of coal, which 

 go by the name of the splint-coal and the coal-rough. These are generally apart 

 from each other about 8 fathoms, the interval between them consisting of the 

 following strata : 



B, Splint Coal generally 5 feet thick. 



C, Fire-clay 1^ fathoms thick. 



D, White Sandstone 4 to 6 feet. 



E, Blue-coloured shale 1^ fathoms. 



F, White slaty sandstone 2^ fathoms. 

 H, Fire-clay 1 fathom thick. 



K, Coal-rough. 



