176 



more than that thickness, has been reduced to a transportable form 

 by the long-continued action of the various denudants, and swept 

 away from that part to form newer strata elsewhere ; and it is not 

 until we get well into Northumberland that we begin again to meet 

 with the edges of the beds that once extended in continuous sheets 

 over all the intervening tract of country, and formed part of one 

 great series of deposits with the coal-field of Stainmoor, of IngletQn, 

 and, in all probability, of the coal-fields further south as well. 



This leads me to remark that although coal is confined in one 

 part of England to beds lying above the Millstone Grit, there is a 

 general tendency throughout all the Carboniferous series for coals 

 to set in at lower and lower horizons as the rocks are traced 

 towards the north-west. Workable coals, some as much as between 

 three and four feet in thickness, occur near even the base of the 

 Millstone Grit near Stainmoor, to wit, at Tan Hill. Coals occur at 

 lower horizons still, elsewhere, and the coal worked at Borradale, 

 on Stainmoor, lies below the Four Fathom Limestone of the Yore- 

 dale Rocks. At somewhat higher horizons comes in the coal 

 occurring in the " Coal Sills," which, as the Survey maps and 

 sections* of the district will shew, form an important part of the 

 coal worked in North Cumberland and the neighbourhood of 

 Hexham. 



Coal, again occurs at yet a lower horizon just over the Border; 

 for the Canobie Coal Field is worked, as Professor Geikie has 

 pointed out, in part of the Cement Stone Series, which occupies 

 an horizon low down in the Carboniferous rocks in Scotland and 

 in the parts of Cumberland and Northumberland extending north- 

 wards from Bewcastle. I have myself t expressed an opinion that 

 the Calciferous Sandstones represent a local expansion of the lower 

 part of our Mountain Limestone ; while others, amongst whom was 

 the late Mr. Ward, consider that they represent a geological 

 horizon even lower than that. 



Now, I have before mentioned that the Carboniferous rocks 

 had been very greatly faulted, disturbed, and denuded before the 



* Sheets 62, Vertical Section, 

 t Quart. Journ. Geol. Soc, vol. for Nov. 1874, p. 394. 



