MR MILNE ON THE MID-LOTHIAN AND EAST-LOTHIAN COAL-FIELDS. 303 



B out of its regular course, has been possibly caused by its proximity to the slip 

 A A', which had shattered or weakened the strata at B' ; but the progressive direc- 

 tion of the original force had been such as to prevent the crack from making a 

 greater deviation, and compelled it to resume its former course towards B". 



(10.) Another important subject of inquiry, regards the amount of vertical 

 derangement of the strata caused by the slips. 



It is obvious, that when the continuity of the strata was broken by a fissure, 

 reaching from the lowermost up to the very highest of the sediment-strata, there 

 would be a tendency in the strata to sink down on the one side or the other of the 

 fissure. Is it possible by any fixed principles to judge on which side of a slip these 

 strata would sink down ? We have seen that nearly nine-tenths of the whole slips 

 in this district run in a north and west direction. The table I have constructed 

 shews, that whilst there are fifty-two slips which throw down the strata 861^ 

 fathoms on the north side, there are thirty-seven slips which throw down on the 

 south side, and that to the extent of only 402 fathoms. The result on the whole 

 is, that the number of fathoms that the strata are thrown down towards the 

 N., is more than double the number of fathoms that are thrown down towards 

 the S. Can any explanation be afforded for these facts ? On this subject I throw 

 out the following views. 



It has been explained, that two causes have operated in producing disloca- 

 tions of the strata — subsidence and lateral pressure. Now we have shewn, that 

 the subsidence must have been greatest towards the north, because subterranean 

 action and volcanic eruption were most prevalent there. Hence when disloca- 

 tions took place across the strata, the strata would, generally speaking, sink more 

 on the north sides of the slips than on the south sides. 



I may here observe, that in the Fife coal-field, described by Mr Landale in 

 his interesting account of it (published in the Highland Society's Transactions), 

 an opposite rule prevails. Mr Landale says that the slips there " are innume- 

 rable ; and with one exception, all the large ones throw up to the north ; and 

 point out to us in the most decisive manner, the very steps by which the county 

 has been raised to its present level."* Now, in the Lothians, the throw tip, as 

 has just been shewn, has been most frequently on the south side of the slips. 

 I have, however, spoken not so much of the side on which the strata are thrown 

 up, as the side on which they are (to use the same form of expression) thrown 

 doimi ; and applying that symbol of expression to the Fife coal-field, then it would 

 appear that the large slips mostly all throw down on the side next to the Firth of 

 Forth, in the same way as happens in regard to the largest of the Lothian slips. 

 In the Lothian district, it appears to me that most of the facts can be explained 

 by supposing that the strata after being broken across, slipped down by their 

 own weight on- one side or other of the fracture ; and it is probable, that the 



* No. 33, p. 346. 



