300 ^'^^ MILNE ON THE MID-LOTHIAN AND EAST-LOTHIAN COAL-FIELDS. 



in the north part of the district. Further, the table of sUps shews, that the most 

 formidable slips — that is to say those which run farthest and produce the largest 

 dislocations, are also in the north pai-t of the district. There are 08 slips which 

 run in a north and west direction ; — and only 2] which run in a north and east 

 direction. 



(8.) Following out the same reasoning, it is not difficult to account for the 

 general direction of the dykes and sUps that intersect the district, — when their 

 several positions are examined. 



Reasoning a jrriori, it is evident that a crack or fracture would originate at 

 and run from the point, where the force or strain was the greatest. If, on the 

 west side of the basin, there was a lateral pressure, which did not act every 

 where with perfect equality, — one part of the whole mass would be pushed more 

 to the east than another part, and the result would be that the cracks would 

 run in an east and west direction. 



This result is susceptible of mathematical demonstration. Mr Hopkins of 

 Cambridge has, in the very able memoir lately pubUshed by him, afforded it. 

 More striking proofs of the correctness of that demonstration, as well as of the 

 truth of many of his deductions, could hardly be wished for, than are exhibited 

 in the district which I am now describing. 



It will be seen on looking at the map, that the dykes and slips all point to- 

 wards the particular trap-hiU or hills nearest them, and which, from being near- 

 est, were probably most instrumental in elevating and dislocating that part of the 

 basin intersected by these dykes and slips. The Niddry dyke, for example, which 

 runs about W.NW. bears on Arthur Seat. The dyke at St Bernard's Well, which 

 is on the opposite side of that hill, also bears on it, running in a direction S.SE. 

 Proceeding farther south, we find the slips cease to bear upon Arthur Seat, and 

 that they point upon other hiUs of trap — such as the Braid and Blackford Hills — 

 they having been the means of elevating tltuse portions of the basin. In short for 

 seven or eight miles along the west side of the district, a series of slips occur, all 

 bearing on the trappean masses nearest to them, and which it is reasonable to 

 suppose, were insti-umental in elevating the strata which these slips intersect. 



It will be observed, that along this side of the basin the slips are, generally 

 speaking, parallel. The reason is obvious. The force which acted upon these 

 seven or eight miles of the basin, did not proceed from one central point or focus ; 

 it acted continuously along the whole of that western side. If it had acted from a 

 single point, instead of a succession of points, the slips must have converged on 

 the common focus from which they originated. 



This last proposition is made very apparent, by attending to the slips which 

 intersect the strata of the Roman Camp, wliich (as afready explained) runs from 

 Tranent, and divides the basin of the Tyne from the basin of the Esk. This 

 ridge does not run farther west than Stobshill, which is on the south-west side 



