66 Mr. N. J. Winch on the Geology of 



3. The cockleshell limestone, not exceeding 20 inches in thickness, 

 and next below the scar limestone. It is of a dark iron-grey colour, 

 and contains besides the encrinal fossil, oyster shells of the diameter 

 of 4 or 5 inches, and other bivalve shells. It crops out in several of 

 the small gills on Aldstone moor, where it does not exceed in thick- 

 ness 20 inches. 



4. The Tyne bottom limestone, the 10th in the series, 21 feet 

 thick. It is an encrinal limestone, consisting of 3 strata, forming 

 the bed of the Tyne for 4 miles from Tyne head to Garrigill gate, 

 and is the lowest bed in which the mines have been wrought on 

 Aldstone moor, though nearly the uppermost at Dufton. 



5. Robinson's great limestone, the lowest in the Dufton section, 

 and 14 fathoms thick. 



6. Melmerby scar limestone, the thickest in the whole formation, 

 measuring 21 fathoms in Melmerby cliff, where it bassets out. It 

 contains the encrinal fossil, and bivalve shells. 



The beds of limestone have been observed to be more regular in 

 thickness throughout the mining field than those of shale or of sand- 

 stone. 



The beds of shale or plate (as it is called) are very numerous, and 

 are found alternating with the rocks of limestone and sandstone. 

 They are seldom so thick as 7 or 8 fathoms ; but the plate sill, which 

 is the lowest bed in the section below that of Dufton, measures 10 

 fathoms. Shale alternating with sandstone in thin layers sometimes 

 forms beds of considerable thickness, (see section of Hely field,) 

 which are called grey beds : when containing laminse of hardstone 

 and iron pyrites it is called a girdle bed. Iron pyrites is found im- 

 bedded in the shales in great abundance, and in various forms j but 

 owing to the high price of fuel and the great distance from any sea- 

 port it cannot be manufactured into green vitriol to advantage. Clay 



