Hind : Carhoniferous Geology. 



and Durham, and the Memohs of the Geological Survey on 

 Parts of Northumberland/ which, though not based on palseon- 

 tological lines, will serve to shew the lithological succession : — 



Calcareous Series. 



Fell Top or Upper Calcareous division (From Millstone Grit 

 to horizon of Great Limestone) 350-1200 feet. 



Calcareous division from the Base of the Great Limestone 

 to the bottom of the Dun or Redesdale Limestone inclusive, 1300- 

 2500 feet. 



SCREMERSTON. 



Carbonaceous Division. — From the Dun Limestone to the top 

 of the Tuedian Grits, 800-2500 feet. 



TWEEDIAN. 



Fell Sandstones. 



Cement Stone Beds and Rothbury Limestones. 



Lower Freestones. 

 Basement Bed in all from 1000-5 100 feet. 



One immense change has taken place with regard to the 

 lower part of the Series, Calcareous deposits being almost 

 entirely replaced by detrital sediments, in which marine fossils 

 are rare. A second, not shewn in the scheme, is the number 

 of seams of coal which are found through the series. 



The division into Calcareous and Carbonaceous is con- 

 venient only, but it has no palseontological basis. The whole 

 of the Calcareous Series I consider belongs to the Upper Dihuno- 

 phyllum zone, together with possibly all but certainly the greater 

 portion of the Scremerston or Carbonaceous division. In the 

 Memoir of the Geological Survey on Berwick-on-Tweed, Mr. 

 Gunn stated (p. 17), that the total thickness of the Calcareous 

 division dow^n to the Dun or Redesdale Limestone is 1500 feet. 

 There must therefore be a very great expansion of the Dibunop- 

 hylhim zone in this area. Probably, however, owing to the 

 detrital nature of the deposit and the relative paucity of lime- 

 stone, deposition took place at a much quicker rate than in 

 areas receiving mainly a pure calcareous or organic deposit. 



The various memoirs of the Geological Survey give lists of 

 fossils from the various divisions of the Carboniferous rocks in 

 Northumberland. The list in ' The Geology of Plashetts and 

 Kielder,' p. 12-15 of the Carboniferous Series is without doubt 

 characteristic of Dihunophyllum fauna, and no other. 



The figures I have quoted as representing the thicknesses 

 of each sub-division are those given by Prof. Lebour (Op. 

 supra cit.), so that the Dihunophyllum zone, most of which is 

 the upper sub-division, has an extent of from 1650-3700 feet 

 throughout which Productus giganteus ranges. 



Nature 1 it 



