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



to the east remained fixed and stable, could not have happened without having 

 produced fractures along the line of the ridge just described. 



This deduction is also consistent with the fact ; for it has been explained in 

 the first part of this memoir, that at Prestonpans the Great Seam of coal which had 

 once been continuous is broken across, and there is a gap or chasm between its 

 ridges of several hundred yards. This gap increases very considerably to the 

 south. At Chalkieside and at Fuffet the limestone which lies below the North 

 Greens — and therefore very far below the " great seam," may be seen broken 

 across, and dipping in opposite du-ections. At this last spot, there is about fifty 

 yards of interval betwixt the edges of the fracture. 



(5.) All the effects now deduced, would follow simply from the sinking of the 

 strata by their own weight. But the production of these effects would be greatly 

 aided, by the play of another power, which must have operated to a certain ex- 

 tent. I allude to the lateral pressure of the igneous rocks during then' eruption. 

 They must have squeezed the whole basin towards the east, and so either have 

 pushed the central parts of the basin down, — or else have caused the strata on 

 the opposite or eastern side of the basin to rise up and form a ridge. It is 

 possible, that the formation of the Tyne basin may actually be owing to this very 

 effect, because it is easy to see, that a ridge would thereby be produced to which 

 the strata on each side would rise. If on the east and south side of that ridge, the 

 strata did not dip down towards the Tyne, at a steeper angle than 20° or 30°, — 

 lateral pressure would not be necessary to explain the facts. But at Cousland 

 they dip towards the SE. at an angle of about 60°, — and at Bhnkbonny they dip 

 to the S. at an angle of about 40°. These facts cannot be accounted for by de- 

 position merely. 



About the middle of this ridge, — and in particular, between Fordel and the 

 Roman Camp, there are several minor troughs, which form, on the map, loops 

 in the line of outcrop, of the coal and limestone. These may be accounted for, by 

 supposing, that there were in some places, two anticlinal lines of elevation. The 

 strata between these Mnes would, of course, be formed into smaU basins. 



The strata are found occasionally along the Roman Camp ridge, in a soft or 

 sandy state. At Bryants, a coal seam, which is known usually to be strong and 

 solid, is so friable and shattered, as to be unfit for working. A thick sand- 

 stone stratum adjoining it, was found to be in the same state. They had been 

 crushed, by the enormous lateral pressure. The pressm-e must have been against 

 the edges or ends of the strata, to have produced the effects obsei-ved. A pressure 

 on the surface of the beds, would have only consoUdated, and not broken them. 



(0.) Having thus endeavoured to shew, what would be the shape and condition 

 of the coal-basin in its several parts, arising ft"om the outburst of the igneous rocks 

 of the districts, I proceed to consider other effects of a more local, though no less 

 interesting, description. 



