MUSEUM OF IHE NATURAL HISTORY SOCIETY. 275 



impure coal with accompanying thin unclerclays. In the Alston 

 Moor and "Weardale districts, where this series is typically or 

 most highly developed, there are nine distinctly defined beds of 

 encrinital limestone, varying from two or three to sixty feet in 

 thickness (Great limestone). These are very uniformly distri- 

 buted over the above districts, and also in the adjoining valleys 

 of the Tees, South Tyne, West Allen, and Derwent, where they 

 occupy, with variations in thickness, the same relative position 

 in the series. In the east and west veins traversing these lime- 

 stone beds are deposited the strings and flats of galena which 

 constitute their chief mineral importance. The sandstones of 

 this division denominated " hazles" have a highly crystalline and 

 metamorphic appearance. The majority of these beds are of 

 marine origin. 



In some of the sandstones and shales the usual plants of the 

 Carboniferous rocks are discovered ; but others are characterized 

 by marine shells and corals. The limestones without exception 

 contain marine shells and corals, and for the most part are 

 formed of minute portions of the decomposed stems of the 

 encrinite. The species most conspicuous are the large cockle of 

 the miners, Proclucta gigantea, which is universally distributed, 

 Orthis resupinata, Spirt/era, and a few other brachiopods, 

 Orthoceras, Encrinites, and a few Corals, as Lithostrotion. Trilo- 

 bites have very rarely been detected. The partings of the shaly 

 sandstones are covered with the burrowings of some, as yet, un- 

 known crustaceans. The fossils of the southern portion of this 

 district have not yet been assiduously collected, but in part of 

 Northumberland the late Mr. George Tate, of Alnwick, carefully 

 collected and preserved the fossils of this division. 



It covers the whole of the western portion of the county of 

 Durham, from the outcrop of the lowest members of the Mill- 

 stone grit series, and the adjoining portions of "Westmoreland, 

 Cumberland, and Northumberland, to the Pennine ridge, down 

 the Western slope of which it extends to the Great "Whin Sill. 

 It stretches through the county of Northumberland, occupying 

 the line of the sea-coast, from the mouth of the Aln nearly to 

 the Tweed. The upper parts of the valleys of the Tees, the 



