316 



MESSRS. A. HARKER AND J. E. MARR ON 



sioii (I.). \Vc give for comparison an analysis of a similar rock from 

 the Christiania district (II.) : — 



I. II. 



SiO. 55-45 57'4ii 



TiO, auclZrO, M3 



X (unknown) 0-12 



CO, 0(X) 0-00 



P,d, trace 



Cl trace 



A1..0, 15-91 17-5.3 



FeA 6-84 0-00 



FeO notestim. 176 



MgO 3-65 1-47 



SrO trace 



CaO 11-50 8-51 



Na.,0 0-10 l-7(> 



; K,0 3-36 8-51 



Li„0 trace 



H,0 105 



Fe'So 0-77 



Ignition (1-30) 



9G-81 100-04 



Specific gravity 2-712 2741 



I. Metamorphosed Upper Coniston Limestone, Wasdale Head Farm ; annL 

 E. J. Garwood. 

 II. Pale violet Kalkhornfels, Grunildrud, near Christiania ; anal. Jannasch, 

 Nyt Mag. Naturvidensk. vol. xxx. p. 303. 



The notable percentage of potash in our rock (though less than 

 in the Norwegian one) must have come from ashy material in the 

 original beds, and the alumina points to the same fact. The potash 

 now exists in the abundant orthoclase of the rock : the percentage 

 of alumina is evidently too high to be contained in the felspars alone ; 

 part of it must be combined in the pyroxene. A rough calculation 

 shows that the amount of quartz in the rock must be about 19 per 

 cent. If we suppose that the rock has undergone no change of total 

 chemical composition beyond the loss of carbonic acid, and that the 

 whole of the lime and magnesia originally existed in the form of 

 carbonates, we find that silica must have formed about 50 per cent, 

 of the original rock, or excluding the calcite and dolomite, 67 per 

 cent. This figure does not seem too high, if, as we believe, the non- 

 calcareous part of the rock was chiefly ashy material of rhyolitic 

 character, with a little clastic quartz in addition. The analysis 

 does not, therefore, prove that silica has been introduced during the 

 metamorphism. 



The phenomena of metamorphism exhibited by the Wasdale 

 Head rocks agree in many particulars with those that have been 

 described in impure calcareous strata near other intrusive masses, 

 such as the Eamberg granite in the Harz *, and the hornblende- 



* Lossen, ' Erlaut. zur geol. Specialk. v. Preiissen ' (1882), Blatt Harzgerode^ 

 pp. 66-73. 



