422 ON THE WHIN SILL OP NORTHUMBERLAND. 



in the neighbourhood of Dudley. Mr. Blackwell was also, he be- 

 lieved, among the first to suggest the intrusive nature of the Whin 

 Sill of Northumberland. It appeared to be a great intruded tongue, 

 not quite horizontal, but approximately so ; aud it was interesting 

 to see the evidence brought forward by the authors proving its oc- 

 currence at various horizons. 



Prof. Hughes thought that the intrusive character of the Whin 

 Sill was proved in the sections seen in Hicup Gill and elsewhere 

 along the same escarpment, as the rocks were altered above and 

 below it, and were seen to be traversed obliquely by it in such a 

 manner as could not be explained simply by the thinning out of the 

 sedimentary deposits. 



He thought that the Brockram and other New-Red deposits of 

 the Eden valley were the shore deposits of the sea further out, in 

 which sooner or later the Magnesian Limestone of the district west 

 of the Pennine range was formed ; that, whatever may have hap- 

 pened in earlier times, there was certainly a great faulting after the 

 deposition of the Lower New Red, so that the cliff, with the Whin 

 Sill exposed in it, did not exist there when the conglomerates 

 known as Brockram were formed ; that the beds into which the 

 Whin is intruded do not occur on the S.W. of the Brockram, though 

 it may be that beds of the same age, but very different in character, 

 may occur further north beyond the main mass of Brockram ; 

 that the Brockram now exposed was derived chiefly from Mountain 

 Limestone further west, so that the absence of Whin in it goes for 

 nothing ; that there is no evidence to show whether or not the 

 Whin has an outcrop under the New Red or runs into it ; and on 

 the whole, except we identify it with the dykes which run across 

 the Jurassic rocks to the east, there is nothing proved in that dis- 

 trict respecting its age except that it must be later than the Lower 

 Carboniferous. 



Mr. Lebour said that Prof. Hughes was right with regard to the 

 absence of the Whin Sill in the southern extension of the western 

 Yoredale rocks. The alteration produced by the Whin Sill differed 

 according to the kind of rock affected by it ; and the difference was 

 probably due to the different conductivity for heat of the various 

 rocks. 



