CHARACTER OF THE WHIN SILL OF NORTHUMBERLAND. 409 



neither desirable nor possible to separate the lower from the similar 

 middle and upper calcareo-carboniferous groups " *. 



In the maps of the Geological Survey, as yet published, all the 

 beds in Northumberland and Durham, below the Millstone Grit, are 

 grouped as the " Carboniferous-Limestone Series." This includes the 

 Yoredales of Phillips and also his Scar- Limestone Series. The lower 

 beds (the Tuedian of Tate, or Calciferous Sandstone of Maclaren and 

 the Geological Survey of Scotland) are not yet surveyed, and it is as 

 yet uncertain where (in Northumberland) the line must be drawn. 

 The Whin Sill is wholly comprised within the Carboniferous-Lime- 

 stone (Bernician) Series of Northumberland and Durham ; it never 

 approaches beds which any one could suppose to be Tuedian. 



3. Bibliography . — The Basaltic rocks of the north of England 

 are frequently mentioned by the older geological writers on the dis- 

 trict ; but the question as to whether the Whin Sill is intrusive or 

 contemporaneous does not seem then to have arisen. The Whin 

 is described as " interstratified " and as occurring in " overlying 

 masses," the latter term apparently referring to areas where the 

 Whin has been exposed by denudation, although the exact sense in 

 which it was used cannot always be determined. 



The earliest paper claiming special notice here is one by Mr. (now 

 Sir Walter) Trevelyan, published in 1823 f . A careful account is 

 there given of the geology of part of the northern coasts of Northum- 

 berland ; a map and section accompany the paper, showing how 

 unevenly and irregularly the Basalt lies amongst the strata in that 

 district. The limestone lying upon the Whinstone is described as 

 being very crystalline towards and at the point of contact. 



Professor Sedgwick printed in the Cambridge Transactions J two 

 valuable papers upon the Trap rocks of Durham. He showed from 

 a consideration of the Teesdale district, in which the position of the 

 Whin Sill is most constant, that there is abundant evidence of in- 

 trusion, the beds below being frequently broken and partially 

 enclosed within the Whin, whilst the beds above are sometimes 

 metamorphosed, this metamorphism of the upper beds being most 

 apparent when the Whin is thickest. 



Mr. W. Hutton is the only writer who has described in any 

 detail the general range of the Whin Sill of Northumberland §. He 

 regarded it as strictly contemporaneous ; and where two or more 

 distinct beds of Whin are known in one district, he supposed that 

 there had been successive eruptions over the ocean-floor. A paper, 

 probably the same, was read before this Society by Hutton, but was 

 published only in abstract ||. In this abstract the author is repre- 



* Geol. of Yorkshire, Mountain-Limestone District, p. 35, 1836. 



t Mem. Wernerian Soc. vol. iv. part ii. p. 253. In the following vol. (p. 475, 

 1826) Mr. Witham describes the basaltic rocks of the north of England, but 

 without throwing any further light on this question. 



X Vol. ii. pp. 21 and 139, 1827. 



§ Trans. Nat.-Hist. Soc. Northumberland &c. vol. ii. p. 187, 1832. (Read 

 Dec. 19, 1831.) 



|| Proc Geol. Soc. vol. i. p. 341, 1832. (Read Dec. 14, 1831. and Jan. 4. 

 18.32.) 



