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



directions of which have been exactly ascertained, there are 94 which he be- 

 tween the north and west points of the compass, and of the remainder 7 run in 

 a direction due west. 



(3.) The sUps are here as in other places more or less vertical. I have heard 

 of none which deviates more than 15° from a vertical plane. This, however, is a 

 branch of the subject on which my information is yet imperfect. 



But though I cannot state the precise angle which the slips make with a 

 vertical line, I have ascertained on which side they deviate from the vertical line, 

 or in other words, towards what point of the horizon they dip. There is a sepa- 

 rate colimin in the table for this information. The point now mentioned is easily 

 ascertained by means of a remarkable law, which prevails here, as every where 

 else, viz. that if a dislocation of the strata has taken place, and the fractiu'ed ends 

 of the strata are no longer opposite to one another, — then it is invariably found, 

 that the side of the slip on which the fractured strata are lowest is the uppermost 

 side of the slip ; — and knowing which is the uppennost side of the slip, and at 

 the same time its horizontal direction, — we learn at once the quarter towards 

 which it dips. Now, in almost every instance where a slip is met with in the 

 working of either coal or lime, it is an object of practical inquiry whether, and 

 how much, the metals are thrown down or cast up by the slip ; — and there are 

 few places where this point has not been most accurately ascertained. There 

 are 78 slips in the district, whose dip I have ascertained by the rule just men- 

 tioned. Of these, 35 dip to the south, and 43 to the north. 



If each of these 78 slips produced an equal derangement of the strata, the 

 result on the whole would of course be to throw the strata doA\Ti more towards 

 the north than towards the south, and in the proportion of the respective num- 

 ber of slips. The strata of the district are, in point of fact, thrown down more 

 to the north than to the south ; — but they are thi-own down to a much larger ex- 

 tent than the above proportion ; for it appears from the table, that, whilst the 

 strata are thrown down by the sUps dipping to the south 385 fathoms, they are, 

 by the remaining slips, thrown down to the north 754 fathoms. 



(4.) These remarks are made with reference to the sMps of the district gene- 

 rally. But the subject is one of such importance, both in a practical and in a 

 scientific view, as to deserve a more particular analysis. 



a. It will be seen from the map, and by comparing the directions of the slips 

 with the croppings of the coal-seams intersected by them, that the slips are in 

 general nearly at right angles to the crop of the coals ; or, in other words, that 

 the rent or fracture of the strata is in the line of the dip and rise. There are no 

 examples of slips, (at least deserving any notice), which run parallel with the 

 a'opping of the strata. 



b. Farther, it will be seen from the map, that where the dip or the direction 

 of the strata continues uniform through a given district, the slips are all parallel 

 to each other. This, indeed, is a corollary which flows directly from the rule 



