209 



of augite granules, lath-shaped sections of felspar, and grains of iron ore- 

 On closer examination an extremely minute quantity of interstitial matter 

 may generally be detected between some of the felspar sections. 



In its composition and structure the rock of the Whin Sill is remark- 

 ably uniform throughout the entire area. The specific gravity is also 

 fairly constant. It varies from about 2*9 to 2'98. (See Fig. 2, Plate XIIL). 



ANALYSES OF THE WHIN SILL. 



I. II. 



Si0 2 ... 51-22 ... 50-71 



. Ti0 2 ... 2-42 1-92 



A1A 14-06 ... 14-78 



Fe 2 3 4-32 ... 3.52 



FeO" 8-73 8-95 



MnO ... 0-16 ... 0-31 



CaO ... 8.33 ... 8-21 



MgO 4-42 5-90 



K 2 1-25 1-39 



Na 2 ... 2.55 ... 2-76 



H 2 6 1-28 ... 1-78 



CO, 0-19 0-25 



P 2 6 5 0-25 



FeSo 0-49 



99-67 ... 100-48 



I. Whin Sill. Cauldron Snout, Durham (TEALL). (D 

 II. Whin Sill. Crags near the Roman Station of Bourgovicus, Northumberland 



Midland Counties. Contemporaneous volcanic products of basic 

 composition occur at two horizons in the Carboniferous Limestone of 

 Derbyshire. They are well exposed in Tideswell Dale, Miller's Dale, in 

 the neighbourhood of Matlock, and in the Ashover Valley. Intrusive 

 rocks occur here and there, and these may be referred with considerable 

 confidence to the same general period. The local name for the igneous 

 rocks of Derbyshire is "toadstone." They are very often amygdaloidal 

 and so highly decomposed throughout their entire mass that it is 

 impossible to make out their original characters. These decomposed 

 amygdaloidal varieties would be termed melaphyre, or diabase-mandelstein 

 on the Continent. Similar decomposed masses occur abundantly in the 

 Midland valley of Scotland and are well exposed on the Island of 

 Inchkeith. In Derbyshire they may be seen in Miller's Dale by the 

 roadside. 



The rock of Tideswell Dale is comparatively fresh. It is exposed 

 in an old marble quarry on the right-hand side of the road leading 

 up the valley from Miller's Dale to the village of Tideswell. It is a 

 distinctly crystalline rock containing large olivines, now for the most 



(1) Q. J. G S., Vol. XL. (1884), p 654, 



