CHARACTER OF THE WHIN SILL OE NORTHUMBERLAND. 411 



before trie British Association a brief outline of the facts now to be 

 detailed *. 



Whilst geologists generally are divided in opinion as to the na- 

 ture of the Whin Sill, those who are also practical miners are almost 

 unanimous in regarding it as contemporaneous. Doubtless this 

 arises from the fact that in the districts which have been most ex- 

 plored by mining the Whin happens to lie with greatest regularity. 

 But frequently this constancy is assumed without proof ; and it is 

 often thought to be proved by reasoning in a circle. The so-called 

 "Little Whin Sill" of Weardale is a case in point. This was 

 always considered to be the " Great Whin Sill ; " and therefore the 

 limestone lying on it was called the " Tyne-Bottom Limestone." A 

 miner would have said : — " This is the Tyne-Bottom Limestone ; and 

 therefore the Whin is in the usual place." Sir Walter Trevelyan, 

 however, long ago proved this to be mistake, and that the Whin 

 of Weardale lies much higher in the series than the Whin of Alston 

 and Teesdalef. 



4. Strati graphical Relations of the Whin Sill. — We have thought 

 it better to select some of the more striking sections which illustrate 

 our views as to the intrusive character of the Whin Sill, than to 

 describe one by one all the sections on which they are based. It 

 must therefore be clearly understood that the evidence here offered 

 represents by no means all that it is in our power to bring forward, 

 but consists of what appears to us to be of sufficient weight to prove 

 our case. 



The portion of the Whin Sill to which the accompanying sections 

 (PI. XVIII.) refer is that which lies between Haltwhistle and 

 Dunstanborough, within which limits it forms an intermittent line 

 of outcrops some 80 miles in length. 



In order to give a key to the relative positions of the horizons 

 with which we have to deal, a diagram, to scale, is annexed. To 

 this is added part of Westgarth Forster's well-known " Section of 

 the Strata" in the Alston-Moor district. This section (from the 

 Tyne-Bottom Limestone upwards), it will be seen, does not hold per- 

 fectly good throughout the district under our notice, chiefly owing 

 to a considerable increase in thickness in the series in Mid North- 

 umberland. 



On entering the county the Whin is for a space lying above the 

 " Great" Limestone, some 700 or 800 feet above its Alston horizon, 

 but returns to its usual Penine position before long, near to which, 

 with fluctuations above and below within about 300 feet, it keeps 

 running at first in an easterly direction, and taking, on nearing the 

 North Tyne, the north-easterly bend to which all the beds of the 

 district are subject. At Low Teppermoor it is seen at about its 

 lowest horizon ; and here a short surface break is very well shown. 

 Thence it continues to the N.E. pretty much along the same horizon 

 till it reaches Swinburne Mill, where another surface break occurs 

 accompanied by a rise of a few feet to the next higher bed of lime- 



* Brit. Assoc. Rep. for 1873, Trans. Sec. p. 92. 



t Trans. Nat.-Hist. Soc. Northumberland &c. vol. i. p. 58, 1831. 



