60 Rev. A. Sedgwick on the Geological Relations and 



fathoms of limestone, they reach the coal-measures, which dip about N. by E. at a considerable 



angle*. 



Beyond Ferry Hill the coal strata decline more and more towards the east, and gradually 

 acquire a dip which nearly conforms to that of the overlying formation. But near the Tyne the 

 whole system of the coal strata is, by a great flexure, made to rise to the north-east; and in 

 that position they appear to pass under the northern extremity of the magnesian limestone. In 

 this part of the range there were formerly no coal-shafts sunk through the limestone ; only because 

 the productive beds were more accessible on the west side of it. But in the year 1822, a most 

 magnificent work was completed near Hetton-Ie-Hole, which, after passing through fifty yards of 

 magnesian limestone, descended down to the Hutton-seum at the depth of 297 yards from the 

 surface: and several similar works have been since undertaken in the same neighbourhood f. 

 (See Plate V. fig. 3.) 



From all these details it follows, that the productive portions of the Not- 

 tinghamshire, Derbyshire, Yorkshire, and Durham coal-fields, which are 

 covered by the maj^nesian limestone, are in no respect deteriorated in quahty 

 by its presence. The formation in its long and generally unconformable range 

 sometimes passes over rich, and sometimes over barren parts of the great car- 

 boniferous deposits ; but these are mere accidents of position, and not effects 

 in any way attributable to the existence of the limestone. Inclined beds of 

 coal when very near the surface may have sustained some injury from the 

 mechanical action which accompanied the deposition of the superior for- 

 mation : but the supposition of any other injury generally affecting the pro- 

 ductiveness of the lower beds, seems to involve nothing less than a physical 

 impossibility. 



These conclusions are in strict conformity with the facts connected with 

 our south-western coal-districts, which are detailed in a former volume of 

 the Society's Transactions (Second Series, vol. i. p. 249 — 280) ; and they are 



* The assertion " that no coal-mine had been seen in Northumberland or Durham under the 

 magnesian limestone" is certainly erroneous. (Geol. Trans. First Series, vol. iv. p. 8.) The 

 principal beds worked under the magnesian limestone in the county of Durham in the places 

 above mentioned are, I believe, the Jive.quarter-seam and the high-main. That the coal-beds 

 generally pass under the limestone cannot admit of doubt ; and there does not appear to be any 

 good ground for supposing that when in such a position they are deteriorated in quality. As 

 this fact is of great importance, it may be proper to add, that at Nunstainton (a few miles to the 

 S.E. of Ferry Hill) a good bed of coal was reached, at the depth of about fifty-eight fathoms, after 

 boring through about forty fathoms of magnesian limestone. 



From the sections near Cowndon, it seems probable that the coal-measures, after passing under 

 the limestone, make a saddle and dip to the S.E. At Ferry Hill, on the S.W. side of all the 

 present works, the coal strata are traversed by a fault, beyond which they are supposed to dip 

 towards the S.E., a direction nearly opposite to that which was stated above. Should this great 

 llexure of the coal strata under the limestone be true, it makes the want of conformity between 

 the two formations still more remarkable, and at the same time explains the appearance of the 

 coal-beds under the limestone at Nunstainton. 



t For the number, relative position, thickness, and provincial names of the several productive 

 beds in the great northern coal-field, see Mr. Winch's paper (Geol. Trans. First Series, vol. iv.), 

 and Mr. Westgarth Foster's section of the coal-measures. 



