Dolotnitization in the Carboniferous Limestone. 105 



of the Dale are really transitions, and are not interbedded with, 

 dolomite, a matter of considerable significance. North-westwards 

 the dolomitization extends for some distance up Long Dale which 

 joins Gratton Dale at right angles. 



Throughout Long Dale, which extends parallel with the strike, 

 I have been unable to see any vertical junction between the lime- 

 stones below and the dolomite above. The vertical change, however, 

 must be fairly abrupt, smce for some distance the beds on the 

 northern side are dolomitic while those on the southern side are 

 normal limestones. The actual lower boundary of the metasomatism 

 here lies under the grass-grown bed of the valley. About a mile 

 up Long Dale the valley swerves a little northwards, and the 

 dolomitization is then seen on both sides, indicating that the 

 metasomatism definitely persists along certaua beds since the dip 

 of the strata remains the same. Westwards, as Friden is approached, 

 lumps of limestone and dolomite are found mixed in scree material ; 

 while still further the dolomitization rapidly becomes less persistent, 

 and good examples of transitions into limestone occur on both sides 

 of the valley. The actual passages from dolomite into limestone are 

 seen to be abrupt. Kernels of limestone, often several feet in width, 

 occur surrounded by dolomitic material. Before the Bakewell road 

 is reached the lower beds have all become normal limestones, and 

 beyond this road the upper doloniitized beds become patchy, and 

 eventually kernels of dolomite in limestone and larger isolated 

 masses, as at Parsley Hay, are all that appears to represent the 

 massive dolomites of Gratton, less than 3 miles distant. West- 

 wards, the field evidences are quite definitely in favour of subsequent 

 dolomitization. Eastwards the matter is less satisfactory. The 

 hilltops above Gratton Dale, a little east of Mouldridge Grange, are 

 overgrown, and I have been unable to trace the dolomitization 

 further. This part of the sequence could, of course, be faulted out, 

 but there is no evidence of this. 



The whole of the dolomitized beds pass more or less abruptly 

 into limestone in an easterly direction, and this abrupt passage has 

 its parallel in the sudden transition of Harborough dolomite into 

 the limestone of Middleton Moor, described in the next section. 

 An important feature that must not be overlooked is the fact that 

 in these Dj beds the dolomitization is extensive and persistent only 

 in the valleys. Eastwards and westwards where the dales give 

 place to higher ground the metasomatism dies out. This is the 

 converse of the dolomitization on the heights near Matlock. 



In their structural and mineralogical features the Dj dolomitic 

 limestones of Gratton resemble, in many ways, the material of 

 Winster. Thus considerable obliteration of bedding planes has 

 occurred ; vesicular weathering is a pronounced feature, and 

 pseudo-brecciation is absent. On the other hand, there are well- 

 marked differences between the materials of the two horizons. 

 That at Long Dale is frequently exceptionally coarse in texture ; 



