Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/83



2. Impressions of Arcæ and Anomiæ. Sowerby, t. 35. On ferruginous sandstone from Allendale and Teesdale.

3. Impressions of Euphorbiæ 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 district 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 above mentioned 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 remarkably well with the toadstone of Derbyshire.

By far the greatest assemblage o£ 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 dodecahedron's, and