148 Proceedings of Philosophical Societies. [Feb. 



Below the coal measures, described in the former part of this 

 paper, occur the lead-mine measures, \Yhich consist for the most 

 part of lime-stone, sand-stone, and whin. The whin is a true trap 

 rock, composed of felspar and hornblende, and is found in three 

 different situations ; first as dykes, or nearly vertical beds intersect- 

 ing the regular strata; secondly, inclosed between the regular strata, 

 and considered in general as one of them, although its thickness 

 varies much more than that of the other strata, the great whin sill 

 being in some places only six fathoms thick, and in others amounting 

 to 20, and even 30 fathoms. Like the toad-stone of Derbyshire, it 

 is not penetrated by any of the metallic veins that abound in the 

 adjacent lime-stone. The third situation in Which the whin occurs 

 is in overlying masses with the external appearance of common 

 coarse-grained basalt, and often shooting into regular columns of 

 considerable magnitude. 



The principal repository of lead is called the Great Lime-stone, 

 about ten or eleven fathoms in thickness, and divided by indurated 

 clay into three distinct strata. It is of a brownish or dark bluish- 

 grey colour, and abounds in encrinites and bivalve shells. From an 

 analysis of it by Sir H. Davy, it appears to be nearly pure carbonate 

 of lime, containing neither magnesia nor alumina, and only about 

 one per cent, of oxide of iron. 



The scar lime-stone resembles the former in external characters, 

 and the fossils which it contains; and is also divided into three strata, 

 the aggregate thickness of which is about five fathoms. 



The tvehle shell lirne-stone is a thin bed, scarcely amounting to 

 two feet, and is characterized by its containing bivalves, like oyster 

 shells, fi ur or five inches in diameter. 



The next bed, called the Tyne Bottom Lime-stone, is an en- 

 crinal lime-stone divided into three strata, of the aggregate thickness 

 of about 21 fathoms. It forms the bottom of the Alston Moor 

 mining-field, but is nearly the uppermost bed at Dufton. 



Below this :uc five other beds of mineral lime-stone, resembling 

 the preceding. 



Between the beds of lime-stone occur numerous beds of sand- 

 stone, varying in structure from completely slaty to solid amor- 

 phous rock fit for mill-stones. Of these the brown ferruginous 

 beds called hazles are found to be much more productive of lead 

 than the others. 



Tiie common lead ore of this district is galena, holding silver in 

 various projwrtions, from two ounces in the fothcr (21 cwt.) to 42. 

 ounces. 'J'iie general average, however, is about 12 ounces. 

 J The lead measures rest upon the red sand-stone, and their total 

 thickness is su})posed to be about 457 fathoms. The metallic con- 

 tents of the veins, besides several varieties of galena, are carbonate 

 of lead, both crystallii.ed, massive, and earthy, phosphate of lead, 

 copper pyrites, azure copper ore, malachite, iron j)yrites, span"y 

 iron ore, blende, calamine, and siliciferous oxide of zinc. The 

 veiu-stones are quartz, several varieties of calcareous spar, coral- 



