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



whole branches exist : there are none on the upper side, but there are several 

 sockets where branches of large size have been, and from which they have been 

 apparently torn off. 



It will be observed, from the description now given, that both of these trees 

 slope in nearly the same direction, having their heads towards the W.NW. If 

 these trees were transported by currents, and Avere at length arrested by their 

 roots, or sticking in silt or sediment, their upper ends, especially if any branches 

 remained on them, would slope upwards in the direction of the current. If no 

 other circumstance interfered, this would undoubtedly be the case ; and if it ap- 

 pear that all or the great proportion of the fossil trees in the district have their 

 tops towards the same quarter, they may be considered as affording a true and 

 unequivocal indication of the direction of the current which transported them. 



I have been unable to learn with anj'^ thing like precision the direction of the 

 other fossil trees found at Craigleith. One was discovered very recently at 

 Granton, the thickest end of which lay in a direction E.NE. 



I have not said any thing of the origin of the limestone, a subject which 

 seems as yet to baffle the skill of geologists. AU are agreed that it was formed 

 at the bottom of an aqueous medium, but, from what som-ce the calcareous in- 

 gredients came, has not been discovered, — some imagining that it has been 

 transported from a distance, like the sediment of shale and sandstone, — others 

 that it has been suddenly produced by chemical agency of some sort. The diffi- 

 culty of the former theory, in such a district as this, is to discover where the cal- 

 careous matter could have come from. There are not, near the district, any older 

 limestones, by the degradation or attrition of which materials could have been 

 provided for the creation of these carboniferous limestones ; and, moreover, they 

 thicken towards the Lammermuir Hills, among which there is not a particle of 

 lime. It is indeed a fact of a very singular character, that the stratum of hme- 

 stone which, in the north part of the district, does not exceed 4 or 5 feet in thick- 

 ness, should regularly and uniformly thicken towards the south, and that, where 

 it is close upon the greywacke range, it should reach a thickness of betw^een 30 

 and 40 feet. In the former part of this memoir, I mentioned another fact, which 

 I think ought here to be kept in view ; — ^viz. that beds of shale, which in other 

 j)arts of the district contain little or no lime, become tow ards the south " bastard 

 limestones." 



It appears to me, that these facts strongly support the theory of chemical 

 agency. Water, when cool, can hold carbonate of lime in solution, provided 

 there is an excess of carbonic acid. But, if heat be applied to the water, so as 

 to drive off a part of the carbonic acid, a precipitate immediately takes place. 

 Now, it is probable that the estuary which covered this district was warmer along 

 the flanks of the hills than elsewhere, and for two reasons, — one is, that it was 

 shallower, in consequence of which, the influence of the solar and atmospheric 



