]Jolo77iitization hi the Carboniferous Limestoiie. Gl 



Winster material. Differences in. composition, specific gravity, 

 and porosity are indicated in the following table, compiled from 

 analyses of typical specimens. 



FABLE SHOWING VARIATION IN CHEMICAL COMPOSITION, SPECIFIC GRAVITY, 

 AND POROSITY OF DOLOMITIC MATERIAL BETWEEN GRATTON AND CROMFORD. 



As far as one can say from the specimens analysed, the greatest 

 variation appears to be in the vicinity of the Wyn Tor. The con- 

 siderable variation in the proportion of magnesium in the material 

 between Gratton and Winster certainly suggests subsequent 

 metasomatism, and although the chemical evidence of the Matlock 

 material might support the theory of contemporaneous alteration, 

 the field and inherent structural evidences are quite against such an 

 explanation. It appears that three distinct modes of metasoinatism 

 may produce material having fairly constant chemical composition. 

 The same conditions which favour the formation of extensive bedded 

 dolomites would in all probability result in the material having a 

 reasonably uniform composition over considerable areas. This would 

 particularly be the case with primarily precipitated dolomites, and 

 might generally be the case, though perhaps not so pronounced, 

 in the contemporaneous alteration of bedded material. Thirdly, 

 nearly complete subsequent dolomitization affecting a relatively 

 small area could produce a constant composition, and I regard the 

 Matlock dolomitization as an example of this type. 



If results of analyses are plotted graphically, the relative proportion 

 of magnesium and calcium at any locality can be seen at a glance, 

 and the dolomitic gradient or rate of increase in magnesian contents 

 per unit distance can be appreciated. Near the Grey Tor, Winster, 



