110 L. M. Parsons — 



brought abruptly against dolomite. Thin sections show organic 

 structures in a matrix mostly non-recrystallized, and no rhom- 

 bohedra are present. It is quite clear from field and petrological 

 evidences that this fault has no relation to the origin of the 

 metasomatism. Apart from all other evidences, the moderate 

 throw of this fault as shown by the presence of a Dg fauna in the 

 higher Harborough beds is fatal to any conception that the massive 

 dolomites of Harborough and Rainster might be a continuation of 

 the thick middle D^ dolomitic series of Gratton Dale, described in 

 Section IV. East of the Hopton roadway, the Hoptonwood Quarries 

 exhibit a considerable vertical section embracing a large portion of 

 the Dj sequence below the lava while lower D^ beds above the lava 

 are seen on Middleton Moor. The shaft of the old Snake Mine 

 pierces other beds lower in Dj, and a table of the strata seen there is 

 given in one of the Survey Memoirs.^ No dolomitization whatever 

 is found in any of the material seen in the Snake Mine, in the 

 Hoptonwood Quarries, or on Middleton Moor. It is evident that the 

 dolomitized beds around Harborough have all passed more or less 

 abruptly into normal limestones somewhere between the position 

 of the Grifie Fault and the Hoptonwood Quarries, a distance less 

 than three-quarters of a mile. Near the High Peak Railway, and 

 further southwards visible exposures indicate that the dolomitized 

 Dj beds here pass rapidly into limestone though the actual lateral 

 contacts are obscured. Along the southern boundary from Hopton 

 to the Great Rake Mine, the dolomite and the underlying limestones 

 have been faulted down to the south. In the absence of borings it is 

 impossible to say how far southwards the dolomitization extends. 

 The faults near the Great Rake Mine have produced lateral shifting 

 of the dolomite pseudo-strata. The junction of dolomite and lime- 

 stone is again quite distinct and along straight lines. The western 

 boundary of the dolomite from GrifEe Walk to the southern extremity 

 near the Great Rake is a weathered termiaation along the strike, 

 the pseudo-strata being modified at one or two places by dip faulting. 

 In the mass west of the Brassington Fault, certain dolomitized 

 D2 beds extend westwards for about 2 miles. In the vicinity of the 

 Rainster Rocks another strike fault is indicated by a straight line of 

 demarkation between dolomite on the west and limestone on the east, 

 while theHarborough Rake produces a well-marked lateral shift in the 

 dolomitic material. Behind Brassington Church are several remnants 

 of limestone in dolomite. Other large remnants of limestone occur 

 west of the Rainster Rocks, and indicate transition in some of the 

 lower dolomites. Owing to these transitions and the White Edge 

 fault, the dolomitization in the Roystone Valley is restricted to the 

 hill-tops along the eastern side, until an extensive dip fault lets 

 the material down, the dolomite then occurring on both sides of the 

 valley. The Roystone fault is one of the most clearly marked in the 



1 North Derbyshire, 1887. 



