Mr. Winch on the Geology of the Banks of the Tisoeed. 131 



engarthdale, in Yorkshire, (Geol. Trans, vol. iv. p. QS,J but neither of 

 these remarkable strata occur in the Lead mine district of Durham or 

 Northumberland, though a part of the same chain of hills ; nor can the 

 identity of Millstone Grit be here depended upon as in Derbyshire, 

 for one bed at least of this apparently well-defined rock, is associated 

 with Coal measures at Hauxley, Widdrington, Ulgham, Berwick Hill 

 near Mason Dinnington, and Heddon-on-the-Wall, and another traverses 

 the country to the westward, from the sea coast in the vicinity of How- 

 ick and Warkworth by the Helm on the Hill, Netherwitton, Roadley, 

 Shaftoe Crags near Wallington, and Stamfordham. Basalt being evi- 

 dently the production of fire, and pervading in an irregular manner 

 rocks of almost every age, does not come within the scope of these re- 

 marks ; so that the similarity of organic remains has at length become 

 the Geologist's chief guide and reliance, in proving or endeavouring to 

 prove, the identity of formations, but if I mistake not, these exuviae 

 will not always warrant the conclusions drawn from their presence. 



