112 L. M. Parsons — 



(3) The outcrop does not resemble the outcrop of a bedded 

 deposit. 



(4) Crystals of dolomite frequently occur in the fault plane and 

 in adjacent cavities. 



Inherent Steuctural and Mineralogical Features. 



Many of the structural characters of the material between Hopton 

 and Roystone are very similar to those of the dolomitic limestones 

 around Winster, hence it will suffice if features common to the 

 material of both districts are enumerated and a few notes added. 



The common features include : — ■ 



Megascopic. — Welding of beds and consequent obliteration of 

 bedding, enlargement of joints, shrinkage, dolomitic stacks and 

 vesicular (differential) weathering. 



Microscopic. — The general tendency to allotriomorphism and 

 considerable variation in size of grain (see PI. VI, Fig. 3), dusky 

 inclusions, interstitial limonite frequently, zonal inclusions of 

 limonite occasionally, and inconclusive " selective " features. (See 

 PL VI, Fig. 4.) 



On the other hand, the Harborough and Rainster material differs 

 from that of Winster in containing no chert, there is no pseudo- 

 brecciation at all, and in the absence of the lava which dies out near 

 the Griff e Fault, there is no question of metamorphic effects. 

 ■Obliteration of bedding is prevalent throughout the whole area, and 

 is nowhere better marked than at the Roystone fault. Stacks and 

 pinnacles of dolomite are more extensively developed than in the 

 Winster area, the Roystone Rocks and Rainster Rocks exhibiting 

 this feature in a striking manner. Vesicular weathering is almost 

 universal. 



Variation in size of grain is indicated by the following figures 

 ■obtaiaed from typical sections : — • 



SIZE OF GRAIN IN DOLOMITES BETWEEN TARWICK AND 



The large idiomorphic crystals in the limestone immediately 

 Ibelow the '' basal " dolomite of the RaLaster Rocks contrast strongly 

 with the allotriomorphic grains in typical material of Harborough, 

 Carsington Pastures, etc. The same mode of magnesiation appears 

 to have produced contrasting results which must have been 



