Northumberland and Durham. 73 



% Impressions of Areas and Anomiae. Sowerby, t. 35. On ferru- 

 ginous sandstone from Allendale and Teesdale. 



3. Impressions of Euphorbias on Freestone from Aldstone and 

 Teesdale. Sowerby, t. 39 & 40. Parkinson, vol. 1. tab. 3. fig. 1. 



Basalt occurs in the mining field either between the regular sills, 

 when it is considered as one of them, or, as it should seem, in 

 overlying positions. The great whin sill in the lead mine sections 

 does not consist of the whin of the colliery sinkers, but is really a 

 basalt, coarse-grained in texture, and composed of white felspar 

 and black hornblende, the latter mineral predominating, and giving 

 to the rock a dark greenish grey colour. This bed is placed in the 

 section at Aldstone at the depth of 159 fathoms, and at Dufton 

 is considered as forming the uppermost stratum ; the miners indeed 

 regard all the beds of basalt which occur in the mountainous dis- 

 trict as ramifications from the great whin sill ; but I do not think it 

 certain that there exists this connexion between the beds of basalt 

 found at the two abovementioned places. The thickness of the 

 whin sill is very irregular, being only 6 fathoms in some places 

 and 20 or even 30 at others. In point of situation it agrees re- 

 markably well with the toadstone of Derbyshire. 



By far the greatest assemblage of basaltic rocks in this part of 

 the district is met with in Teesdale from the source of the Tees to 

 Eglestone. At Caldron snout, situated on the moors 10 miles 

 above Middleton, a basaltic ridge crosses the river, and occasions a 

 succession of cascades for the space of 596 yards, which form a 

 fine contrast with the pool of still water or wheel above the falls. 

 It was here immediately under the basalt that the Rev. J. Harriman 

 discovered small white garnets ? crystallized in dodecahedrons, and 



Vol. iv. k 



