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



whole branches exist : there arc 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, ft'om the description now given, that both of these trees 

 slope in nearl^^ the same du-ection, having their heads towards the W.NW. If 

 these trees were transported by currents, and were 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- 

 l)ear that all or the gi-eat 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. 



1 have been unable to learn with an}' thing like precision the direction of the 

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

 Granton, the thickest end of Avhich 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 baftle the skill of geologists. All are agreed that it was formed 

 at the bottom of an aqueous medium, but, from what source 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 ai-e 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 Ume- 

 stone which, in the north pai-t 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 between 30 

 and 40 feet. In the former pai't of this memoir, I mentioned another fact, which 

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

 })arts of the district contain little or no lime, become towards 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 hiUs than elsewhere, and for two reasons, — one is, that it was 

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



