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



same theory may be sufficient to account for most of the phenomena in Fife ; 

 though it is quite possible (as Mr Landale supposes), in regard to some slips 

 which are in the immediate neighbourhood of trap-hills, that the strata were 

 actually lifted up on one side, whilst they stood fast on the other. 



There is another important fact connected with the derangement of strata 

 by slips, which appears to be established by the table in the Appendix. In the 

 Lothian basin, the amount of derangement or displacement of the strata is found, 

 generally speaking, to increase towards the dip of the strata. The reason is pro- 

 bably to be found in the circumstance, that the intensity of the force caused by 

 subsidence was greater than that caused by elevation. The latter force would act 

 at or near the sides of the basin, where the trap hills occur ; and all the slips 

 produced by that force, would exhibit a larger amount of dislocation towards the 

 crop of the strata. The former force would act chiefly in the central parts of the 

 basin, and the fissures caused by it would increase in amount of dislocation to- 

 wards the centre. 



Many of the phenomena, described in the previous part of this Memoir, are 

 accountable, on the supposition either of an elevating force acting alone, or a sub- 

 siding force alone ; — as, for example, the occurrence of ruts and scratches on the 

 sides of slips. But these appearances in the Sheriffhall slip, (which run not in a 

 vertical but in a slaiiting direction, forming an angle of 20° or 30° with the ho- 

 rizon), show, that this force acted in a manner neither precisely vertical nor pre- 

 cisely horizontal, and that the}^ were undoubtedly caused by lateral pressure. We 

 have shewn, that some of the slips were formed by an elevating force, and others 

 by the force of subsidence. The Sheriffhall slip was probably produced by the 

 latter force : — for the strata on the north or lowest side are near the slip, all tilted 

 up, and much shattered. 



There are many other interesting phenomena connected with slips, Avhich I 

 am constrained to pass over. It would be detaining the Society too much with 

 mere details, to dwell longer on the subject. I cannot leave it, however, without 

 adverting to one phenomenon, which distinguishes the slips from the dykes of this 

 district. I formerly adverted to the fact, that along the trap-dykes there is no de- 

 rangement of the strata on either side ; and that it is only along slips, that the 

 strata are thrown down or cast up. This fact is the more curious, if it be true 

 that slips and dykes have both been produced by the same cause, viz. violent 

 subterranean action. This action, we have seen, was occasioned, or at least ac- 

 companied, by great accumulations of trap in a state of fusion, which were pressed 

 upwards against the superincumbent sedimentary rocks. One consequence of the 

 enormous weight and pressure which the igneous matter had to sustain, must 

 have been to force it up — not only into the soft strata of clay and shale, and thus 

 form layers or beds between the harder 3irata, — but also into the vertical cracks 

 and chinks formed in the strata by their elevation and subsidence. By these 



