A 



78 Mr. Forster's Observations on Ratcheugh Crag. 



the Limestone) ; an idea which is strengthened by the stratum imme- 

 diately under the Basalt presenting the appearance of a Coal thill. In 

 this quarry, as at Ratcheugh Crag, the Limestone, Shale, and Basalt are, 

 in point of incUnation, perfectly comformable to each other ; dipping to 

 the S. E. at an angle of 17°. 



The Dyke, which I have considered as cutting across the Cliff, and 

 producing the remarkable difference in the sections, is, I think, an up- 

 cast to the N. E. Ratcheugh Crag will, therefore, be on its rise, and 

 Snableases Quarry on its dip side. That the Basalt overlying the Lime- 

 stone in Snableases Quarry, does not appear above it in Ratcheugh Crag, 

 may be owing to the elevation on that side, and the great thickness of 

 the Basalt under the Limestone in Ratcheugh Crag may, perhaps, be 

 attributed to the same cause. To this Dyke, indeed, I should have 

 considered that the whole of the Basalt in the vicinity owed its origin 

 (conceiving it to be an overlying mass similar to that at Bolam, in the 

 County of Durham), but for the reasons already mentioned in favour of 

 its being a continuation of the Dunstanborough range, and tlie addi- 

 tional evidence of its extent, afforded by the existence of a considerable 

 tract of Basalt, about three-quarters of a mile to the N. W., capping an 

 eminence called Harlow Hill, and appearing to conform, in range and 

 direction, to the bed at Ratcheugh ; thus exhibiting a much more ex- 

 tensive formation than our present knowledge of them would warrant 

 us in attributing to Basaltic Dykes. As they are phenomena, however, 

 concerning which much is probably yet to be learnt, I do not by any 

 means presume to propose limits to their operations, and the principal 

 object of the above observations is to put the Society in possession of 

 the Jacis, leaving the causes of the appearances, I have endeavoured to 

 describe, for abler and more extended investigation. 



Newcastle, May Yl, 1830. 



