GEOLOGICAL LOCALITIES. 29 



In Yorkshire, and indeed as far as Alston, the division is easily understood, but further 

 north it can no longer be recognised, for two reasons firstly, the Whin Sill ceases to be 

 interbedded at the same horizon, and intrudes into higher levels ; and secondly, the Tyne- 

 bottom Limestone ceases to be specially recognisable owing to the intercalation of new beds 

 of limestone and the thinning-out of old ones above and below it. The base line of the 

 Yoredale Series, therefore, whether it be taken as the Great Whin Sill or the Tyne-bottorn 

 Limestone, fails altogether in the northernmost portion of its area. These remarks are 

 needed because in geological maps, otherwise reliable, everything above the Whin Sill is 

 coloured " Yoredale" as far as the Millstone Grit, and all below is coloured " Carboniferous 

 Limestone " proper. The Little Limestone, Great Limestone, and Four-fathom Lime- 

 stone, are all undoubted representatives of portions of the Yorkshire Yoredales, but in 

 following the maps one may find an easily identified horizon, such as that marked by 

 one of the beds containing Saccamrnina, sometimes coloured as Yoredale, sometimes as 

 Carboniferous Limestone proper, and the Great Limestone is in much the same case. 



NORTHUMBERLAND. 



Foraminifera are found 



In the " Eidsdale Ironstone Shale " (30 feet), a bed about two thirds down in the 

 " Bernician " Limestone series [Scar] at 



1. The Ridsdale Ironstone workings, in the shale heaps and old 



quarries. Material collected by Mr. Lebour. 



In tie "Bottom Limestone" (17 feet) of the Ridsdale Ironstone district, which lies 

 above the shale, from which it is separated only by a bed of sandstone 11 feet thick 

 [Scar], at 



2. Skellygate, Ridsdale, from old pits. Material collected by Mr. 



Lebour, and specimens in the Rev. W. Howchin's collection. 



In partings of calcareous shale in a thick bed of limestone, about 800 feet above the 

 last [Scar], at 



3. Colster Cleugh in the bed and banks of the burn about two miles 



east of Elsdon. Material collected by Mr. Lebour. 



