112 DR. J. W. EVANS OK" THE ROCKS OF THE [Feb. I906, 



was estimated as ferric oxide, although much of it must have been 

 present in the ferrous state. 



Percentages. Molecular proportions. 



Si0 2 0-68" -0113 



A1 2 617 -0605 



Fe o 10-75 -1344 (of FeO) 



CaO 4-06 -0725 



MgO 191 -0477 



C0 2 5-76 -1309 



Total 29^33 



The material analysed appears to contain rather less carbon- 

 dioxide, and more iron, than that dealt with in the general analysis. 

 The silica taken up probably represents only a small proportion of 

 that which is present in the silicates attacked by the acid, the rest 

 remaining as gelatinous silica. 



The chlorite (delessite) will account for most of the dissolved or 

 gelatinous silica and the alumina, as well as for much of the iron- 

 oxide and magnesia. Some of the iron-oxide is no doubt derived 

 from the solution of the magnetite. The rest of the iron-oxide, 

 magnesia, and lime, is derived from the carbonate, which is appar- 

 ently a variety of ankerite. The labradorite and micas were, no 

 doubt, also attacked to some extent by the acid. 



The large amount of carbon-dioxide present shows that the 

 rock has undergone considerable alteration, thus confirming the 

 microscopical observations. Comparatively-little water is present, 

 much less than if the olivine had undergone the usual process of 

 serpentinization. Part of the bases appear to have been removed 

 from the orthosilicates (olivine and the anorthite-portion of the 

 labradorite), and accumulated as carbonates in the cavities. Some 

 silica and alkalies may have been.lost; but, on the whole, the chemical 

 composition of the rock after the subtraction of carbonic acid and 

 water will, I believe, represent very fairly its original composition. 



According to the American c]assification, the rock would in that 

 case be an an dose. Its analysis is very similar to those yielded by 

 basalts from Kilauea (Hawaii) and Ferdinandea Island (Graham 

 Sunken Island) between Pantellaria and Sicily. 1 



Basalt, Basalt, Theotoniv. 

 Kilauea. Ferdinandea Id. Without H 2 § CO.,. 



SiO, 48-71 49-24 48-04 



TiO; 1-81 ... 0-36 



A1 3 .... 18-87 19-06 19-66 



Fe 2 3 3-18\ 11ilR 1^71 19 . 1n 4-461-.,^ 



FeO. 8-00j 111& 10-33 r 210 7-32j U ^ 



MgO 4-85 5-00 J 5-84 



CaO 9-87 8-75 8-39 



K 9 152 119 1-50 



Na 2 4-15 3-89 3"96 



H 2 ^ 0-6 3 MnO-32 2 



100-96 9980 10000 



1 H. S. Washington, ' Chemical Analyses of Igneous Eocks ' U.S. Geol. Surv. 

 Prof. Paper No. 14 (1903) p. 282. - With S=0"13 & F=0'04 ; less O = 0-02. 



