Dolomitization in the Carhoniferous Limestone. 113 



determined bv other inherent factors as suggested above (cf. 

 Figs. 2 and S/Pl. VI). 



Zonal inclusions of limonite are uncommon, but some of the 

 Harborough dolomite exhibits features very similar to those of the 

 Complex-subsequent T>^ doloniitic material of Gratton Dale. Fig. 4, 

 PI. VI shows coral structures (Lithostrotion) replaced by dolomite 

 free from zonal limonite inclusions, but the matrix mostly 

 contains dense zonal growths of limonite. (Compare with Fig. 3, 

 PI. IV.) Recrystallized calcite occurs within the spaces between 

 the coral septa. Dolomitization at two different periods is indicated. 

 " Selective " features are varied and contradictory. In examples 

 like that just mentioned, both coral and matrix are almost com- 

 pletely dolomitized, but with dolomite of different types, presumably 

 of different period. In other cases corals are partly in calcite and 

 partly in dolomite, while the matrix is mostly dolomitized. The 

 limestone below the Rainster Rocks shows rhombohedra scattered 

 indiscriminately through both matrix and organic structures. 



/{OYSTOME RAINSTER LONCCLtfFE MANY- HARBORO' HOPTON MlOUiETON ^ 



W. ROCKS ROCKS STACKS STONIS ROCKS TOP MOOR t 



/<?<? 



Af/l£$ ^ 



Fig. 5. — Graphs illustrating variation in chemical composition and porosity of the 

 dolomites between Parwich Moor and Wirksworth. 



The Presence and Condition op Fossils, 

 The general condition of organic remains, and the varied nature 

 of " selective " phenomena so closely agrees with the corresponding 

 features found in the material of Winster and Matlock that the 

 remarks made in Section III equally apply to the material of the 

 Harborough and Rainster dolomites. 



Chemical Composition and Porosity. 

 Chemically, the bulk of the material between Parwich and Wirks- 

 worth resembles a true dolomite in having a high proportion of 

 magnesium. Numerous analyses of typical specimens from various 



VOL. LIX. — NO. III. 8 



