BY HUGH MILLER. 301 



has said of the sea that ''upon a basis of unequally-resisting 

 materials" it must work unequally. But this is true in a much 

 greater degree of every other tool employed in earth-sculpture. 

 It might be expected, then, that when the edges, so to speak, 

 of the various natural tools were being examined as possibly ori- 

 ginative of the features of the " Crag-and-Tail," the glacial tool, 

 once so extensively used among the rocks of all I^orthern Britain, 

 should not have been forgotten. In 1866 the Rev. 0. Fisher 

 advocated glaciers as probably connected with the baring of hard 

 rock-ridges into scarped forms.^' More recently also, Mr. Grood- 

 child, of the Geological Survey, has contended for a similar 

 origin for the limestone terraces of the Yorkshire dales. f Feeling 

 convinced, from previous examination, of the identity of these 

 terraces with the less pronounced ones of ITorth Tyne, and 

 through them with the outlying escarpments, which graduate 

 into the valley, I endeavoured to test Mr. Goodchild's argu- 

 ments. These observations formed the nucleus of this paper. J 



Between the Tynes a glacial sheet over-rode the watershed of 

 the country from the westward, moving nearly parallel with the 

 ridges. Here if anywhere, therefore, it might have ploughed 

 out the furrows. Was it in truth, then, the great ice-plough of 

 the frost-giant that left this gigantic ' ' rig-and-f ur ?" I have 

 no hesitation in replying in the negative. To carry out the 

 analogy of a plough the ice must at least never have driven per- 

 sistently against the face of the furrows. Yet only a few miles 

 eastward, in the IN'orth Tyne valley, such was its direction, and 

 must have been so, guided by the valley, during a great part of 

 the period. Crags like the remarkable headland above Barras- 

 ford must have largely borne the brunt of its force ; which must 

 have tended, if giacialists such as Dr. James Geikie and Profes- 

 sor Green are accepted as judges, to plane them down. This view 

 is supported by sufficiently clear proofs of the pre-glacial origin 

 of the escarpments. The occurrence in the ridges of narrow 



* Geol. Mag., 1866, p. 48!!, t Geol. Mag., 1876, p. 32S. 



X Geol.Mftg., 1876, p. 23. Mr. Qoodchild'g papers wore professedly Intended to "ovokc 

 criticism," but I may say that ncitlicr to mo, nor to two criticisms subsequently published 

 by my colleagues, Messrs. Gunn and Dakyns (Geol. Mag., 1876, p. 97, and 1877, p. 17) 

 has there been any rejoinder. 



