14 A NEW FLOEA OF 



3. The Millstone Grit, which underlies the Mountain Lime- 

 stone, can scarcely be ranked as a distinct formation, for it differs 

 but little from the Coal Measures, excepting in its feeble develop- 

 ment of coal. It is composed of sandstones and shales similar to 

 those in the Coal Measures, and like them, too, it has no lime- 

 stones or calcareous beds, and but few and doubtful indications 

 of any marine conditions. In this group we include all the beds, 

 from the top of the highest limestone, with marine fossils, to the 

 base of the Brockwell Coal, the lowest workable seam in the Coal 

 Measures. The thickness in I^orthumberland is about 500 feet ; 

 and this corresponds pretty nearly with Forster's section of the 

 formation southward of the Stublick Dike. The characteristic 

 beds are thick gritty sandstones, which sometimes have supplied 

 millstones, and hence the name Millstone Grit. Such beds are 

 made up chiefly of rounded pebbles of quartz and felspar bound 

 together by a siliceous cement : some pebbles in the rock are as 

 large nuts, and some few an inch in diameter. At Warkworth 

 this rock, in some parts, is bound by a calcareous cement, and 

 here and there appear grains of protoxide of iron and garnets. 

 In borings made at Shortridge, two coal seams, each 6 inches 

 thick, were passed through. The proportion of siliceous rocks 

 to the argillaceous in this group is about six to four. Sigillaria, 

 Stigmaria, Favularia, and other Carboniferous plants, occur in 

 the' sandstones ; and at Berling Carr there are tracks and casts 

 of annelids in slaty sandstones. 



These beds in Northumberland range south-south westwards 

 in a harrow zone, from 2 to about 5 miles wide, in the same 

 direction as the Mountain Limestone, on which they rest confor- 

 mably, from near the mouth of the Aln to the Tyne ; but beyond 

 the Tyne they are, through the influence of the Stublick Dike, 

 deflected westward, parallel with that dike, to the borders of the 

 county. Some of the high fell lands of Northumberland south 

 of the Stublick Dike and of the western parts of Durham, are 

 capped by Millstone Grit. North of the Tyne it reaches an alti- 

 tude of only 460 feet ; but in this southern district the Grey 

 Millstone aj^pears on ther- mountains between Wolsingham and 

 Stanhope. The Grindstone Sill, another characteristic bed, is 



