C. E. Be Ranee — Mineral Veins in the JSforth-ioest Country. 303 



other small plates which cannot be distinguished from the former 

 either in size or form. These, however, possess no pores ; and 

 whether they were arranged alternately with the poriferous plates, 

 or formed part of the base or summit of the test, it is impossible to 

 determine in their disjointed condition. Both sets show the over- 

 lapped portion of the plate very distinctly. The plates of AtcIkbo- 

 cidaris are thinner than similar plates in other species of Cidaridce 

 constructed upon the normal plan. This feature, taken along with 

 the overlapping characteristics of the plates, may have given more 

 flexibility to the test, like that observed in Calveria. If this were 

 the case, and the plates held loosely together in the living animal, it 

 may help to explain how very seldom it is that we find a specimen 

 preserved with all its parts in position. 



Sections of the larger spines of ArcTioeocidaris, which I have 

 recently prepared, show that they were tubular, the hollow interior, 

 now filled with carbonate of lime, being a quarter of the diameter 

 of the spine. In this other characteristic it also agrees with the 

 Diadematidce and the other species with overlapping plates noticed 

 in the Magazine. 



Vn. — On the Occurrence of Lead, Zinc, and Ikon Ores in some 

 EooKS OF Carboniferous Age in the North-west of England. 



By Charles E. De Eance, F.G.S. ; 



of the Geological Survey of England. 



{Concluded from the February Number, p. 74.) 



PART II. 



East Cumberland. — In the Cross Fell and Alston Moor district the 

 Mountain Limestone is split up into numerous beds of limestone, 

 sandstone, and shale, the thickness and character of which are well 

 known through the local names given to each horizon by the miner, and 

 from the writings of Messrs. Westgarth Forster, Sopwith, and Wallace. 



The chief limestones in the Alston Moor district, down to the 

 Great Whin Sill, a sheet of probably intrusive basalt, are the Little 

 Limestone (20 feet below which are two Coal-seams, 18 and 12 inches 

 thick respectively); the Tumblers or Great Limestone, about 70 feet 

 thick ; the Scar Limestone about 30 feet ; and the Cockleshell 

 Limestone about 18 inches, full of Pr o ductus ; the Tyne-bottora 

 Limestone, about 24 feet, resting on a shaly bed, which occasionally 

 has a thin coal, which at Smitter Gill I found to be turned into an 

 impure graphite, resting on the Great Whin Sill, which at Tynehead 

 is 110 feet, but at Providence vein on the Tees considerably thinner. 

 Of the Alston Moor beds, about 200 feet consist of limestone, 350 of 

 sandstone, and 520 of shale ; some of the latter beds are extremely 

 well characterized, and maintain their thickness over a large area, 

 like the Tyne-bottom plate, only 50 feet in thickness, overlying the 

 Tyne-bottom Limestone. There are several limestones below the 

 Great Whin Sill, extending through some 900 feet of measures, 

 the chief of which is the Jew and the Melmerby Scar Limestone, 

 124 feet in thickness. 



The very remarkable fault known as the " Great Sulphur Vein " 



