The Lower Carboniferous Rocks of Cumberland. 523 



some alumina is still unaccounted for, this is given the requisite 

 amounts of lime and silica to form anorthite. Ferric oxide is then 

 combined with the corresponding amount of ferrous oxide for 

 magnetite. The residual lime, together with ferrous and magnesium 

 oxides in the proportion in which these two are left, yield the meta- 

 silicate diopside, while the rest of the ferrous oxide and magnesia 

 enter into combination with silica as the orthosilicate olivine. 



By the above method a somewhat conventional representation 

 of the muaeral composition of the rock is obtained. It is probable 

 that the figure for analcite is too high, owing to the presence of other 

 hydrous minerals. Further, there is no soda available for the 

 calculation of the amount of alkali-bearing pyroxene present. 

 Diopside, as such, does not occur in the phonolite. 



•The Low^er Carboniferous Rocks of Cumberland. 



By K. W. Earle, M.Sc, F.G.S. 



/^N glancing over back numbers of the Geological Magazine 

 ^^ after eight months' residence abroad, I have been much 

 interested to find a paper by Mr. C. Fidmonds on the Carboniferous 

 Limestone of West Cumberland.^ 



I myself Avorked in this district in connexion with a more 

 ambitious paper on the whole of the limestone series from Penrith 

 via Caldbeck to Egremont, which paper formed the subject of a 

 communication to the Geological Society last November. It is 

 needless to say that at the time of my work I had no idea there was 

 an indej^endent observer in the field, or I should not have devoted 

 much time to his area. Such duplication of field work, though 

 regrettable, is perhaj)s, however, not entirely wasted if the second 

 observer is able — as I am in the present case — to confirm the con- 

 clusions of the first by independent mapping. 



1 Geol. Mag., Vol. LIX, 1922, pp. 74 and 117. 



