MR MILNE ON THE MID-LOTHIAN AND EAST-LOTHIAN COAL-FIELDS. 285 



existed in the grey wacke group as much sihceous as aluminous matter, the re- 

 sult of denudation, in these circumstances, would have been, not alternate layers 

 of sandstone and shale, but a confused mixture of both in one and the same 

 mass. 



It is infinitely more probable that the elements of these several strata were 

 derived from different quarters. Thus, it may be supposed that the siliceous 

 matter was washed down from the primitive formations situated to the north and 

 north-west, in Perthshire and Stirlingshire, whilst ahiminous matter was washed 

 down from the gi-ey wacke hills situated to the south; and that these several 

 supplies were brought down at different periods, so as to give time for the depo- 

 sition of one kind of sediment before the arrival of another kind. This hjrpo- 

 thesis as to the particular districts from which the elements of the shales and 

 sandstones have respectively come, is, of course, little better than conjecture, 

 and is adduced merely in illustration of the possible explanation. It is, how- 

 ever, a confirmation of it, that the siliceous matter which pervades the district 

 is, on the whole, much more abundant than the aluminous matter, and that the 

 sandstone rocks are much thicker in the north-west part of the district than in 

 the southern parts. From the same source, must of course have been derived 

 that remarkable " saddle-back" of sandstone which I have more than once al- 

 luded to as running from New Craighall towards the south, and which has been 

 deposited exactly in the direction to have been expected, if the supply of sili- 

 ceous sediment came from the north. 



It is proper, however, to observe, that this conjecture as to the arenaceous 

 sediment having been brought from the west, is inconsistent with the position of 

 the fossil trees imbedded in the sandstone rocks. In 1830, a tree was excavated 

 from Craigleith quarry, 59 feet in length, having a diameter of 5 feet at its lower 

 end, and 2 feet at its upper end. The tree dipped S. 70° E., at an average angle 

 of 34°. The strata in which it was deposited dipped towards the E.NE., at an 

 angle of about 13°. It seems probable, that the whole strata of this quarry have 

 been raised by Corstorphine Hill ; — on which account, we may assume, that the 

 original dip of the tree was about 28°. It may be added, that the lower end had 

 some appearances of roots, — and at that end, there was a sort of trough in the 

 strata : — that is, they there suddenly dipped on each side of the tree towards the 

 south and north. 



In 1833, another fossil tree was discovered, about 300 yards to the west of 

 the former. It is 32 feet in length ; — ^but it has not yet been entirely excavated. 

 The diameter of its lower end is about 3 feet, and of its upper end about 1^ foot. 

 This tree dips S. 50° W., at an angle of about 46°. The strata in which it is de- 

 posited dip E. by N., at an angle of about 25° ; — so that its original dip may be 

 assumed at 32°. On several parts of the trunk, branches or the remains of 

 branches are very apparent. It is only on the under side of the tree that any 



