THE BRITISH NATURALIST. 



3 



THE GEOLOGY OF MILLER'S DALE. 



BY D. S. STEUART. 



The dale is situated in the north-west of Derbyshire, and a little to 

 the east of Buxton, whence it may be reached in a few minutes via the 

 Midland Railway. The outlines of the district are mostly smooth and 

 undulating", with gently rounded slopes, giving the landscape a somewhat 

 tame and monotonous appearance. These features are apparently the 

 effect of river and atmospheric action on the Millstone Grit, a composition 

 of hard coarse sandstone interlayered with alternate beds of shale and 

 softer sandstone ; resulting in the formation of long unbroken slopes 

 gradually inclining in the direction of the dip, and terminating in cliffs or 

 " edges " overlooking broad valleys, which the streams at the bottom 

 have hollowed out from the soft shale beds beneath. 



No sooner, however, do we come to inspect the limestone " valleys," 

 than we are at once struck by the contrast they offer to those of the Mill- 

 stone Grit ; indeed the word "valleys" is in this case misleading - , we 

 should rather substitute the words " dales " or ravines, many of which 

 are of wild picturesque beauty, especially the one in question. 



For here the river has in many places cut and worked its way through 

 the solid limestone, its erratic and winding course bounded on either side 

 by steep weather-worn cliffs, clothed and beautified with innumerable 

 shrubs and bushes, and luxuriantly carpeted with ivy and other creeping 

 plants, a pleasing relief from the monotonous grey of the limestone rocks. 

 Having obtained some idea of the lie of the land, let us now consider the 

 agents which have been at work in bringing about these changes, and 

 the way in which they have accomplished them. The chief constituents 

 of the dale are the igneous rocks " Dolerite " and " Toadstone," prob- 

 ably a corruption of the word " Todstein " {lit. dead-stone), called by the 

 miners "channel," and the "Carboniferous Limestone," which latter 

 occurs in immense quantities / attaining in places a depth of 5,000 feet and 

 rising as high as 300 feet, frequently intersected with beds of igneous 

 rocks and shales. 



The Limestone itself is chiefly composed of calcium carbonate or calcite, 

 and a double carbonate of calcium and magnesium called " dolomite." 

 It belongs to the carboniferous and coralline Limestones, containing large 

 numbers of corals and other fossils, conspicuous amongst which are the 

 " crinoids " or sea-lilies, with long jointed columns supporting a simple or 

 complex cup surrounded with well-developed arms, reminding one some- 

 what of those of a starfish. 



These vast beds of limestone were formed long aeons ago down in 

 the depth of the ocean, by the continual accumulation of carbonate of 

 lime supplied in the form of shells, foraminifera, and other marine 



