56 L. M. Parsons — 



sense, but not a normal outcrop stratigraphically. Since we are 

 concerned with a problem essentially connected with bedded 

 material having definite horizons, it may be convenient to employ 

 the term pseudo-strata to denote any area of dolomitization in which 

 the metasomatism either changes from one horizon to another or 

 fails to persist along a definite horizon. Some distance eastwards 

 from Bonsall Moor Farm all the beds between the two lavas consist 

 of non-dolomitic limestones extending via Jughole Wood towards 

 Masson Hill. For a distance of about 3 miles normal limestones 

 have entirely replaced dolomitic material of Winster on the west 

 and of Masson Hill on the east. Here is one of the most marked 

 lateral transitions in the district. Near Jughole Wood, as every- 

 where east of Wensley, none of the limestones above the upper lava 

 exhibit any traces of dolomitization, and at Jughole the contact 

 of the lava with the normal limestones below is well seen. Further 

 south-east, as Masson Hill is approached, patchy dolomitization 

 makes an appearance between the two lavas, while on the heights 

 of Masson itself a considerable thickness of dolomite is seen under- 

 neath and in contact with the upper lava. In Matlock Dale the beds 

 are brought down to the river by folding, and in the quarries near 

 the river normal limestones are seen immediately under the upper 

 lava. Here is another striking lateral transition of dolomite on 

 Masson Hill into limestone in the valley below. It is a curious fact 

 that with the exception of the Upperwood Slopes further south, no 

 dolomitic material comes down into the valley, though the beds are 

 repeatedly brought down and taken up again by folding. Apart 

 from small dolomitic patches, the limestones on all horizons on the 

 eastern side of the river are devoid of dolomitization. On the 

 western side of Masson Hill the metasomatism changes from the 

 beds immediately below the upper lava to a lower horizon. South- 

 wards from Masson the dolomitic area extends past Ember Farm, 

 towards the Upperwood Slopes. 



The metasomatism changes horizon gradually as far as Ember 

 Farm, where it has descended to within a short distance of the lower 

 lava. South of this farm, however, the dolomitization leaves the 

 lower beds and the lower boundary of metasomatism rapidly 

 ascends the sequence. Probably nowhere else in the whole area 

 does the pseudo-strata exhibit such a steep horizon gradient. At 

 Upperwood the beds dip towards the river, and the dolomitization 

 extends into the valley, attaining here its greatest vertical extent 

 in the immediate neighbourhood of Matlock, all of the beds between 

 the two lavas being affected. The ground further south is largely 

 overgrown and the metasomatism is traced with difficulty. 



Inherent Structural and Mineralogical Features. 



Megascopic Characters. 

 The material of the Tors and of the escarpment near Winster 

 consists of massive blocks and stacks of rock often several feet 



