62 PEOE. T. G. BONNEY ON THE [Feb. I9O3, 



brought up in large lumps by the basalt, but also is scattered through 

 it in small grains. In this way I understand Prof. Vogt to explain 

 the presence of the titaniferous magnetite in olivine-hyperite at 

 Taberg, 1 the nickel-silicate in serpentine in New Caledonia and the 

 ores of that metal in other places mentioned in his paper. In 

 processes of mineral separation the residue becomes, sometimes more 

 basic, sometimes more acid, and when separation has taken place 

 on a large scale, either the former may contain fragments of the 

 latter, 2 as in some Scandinavian cases, or, as at Cogne and Ovifak, 

 the reverse may occur. In like way we sometimes find fragments 

 of a granitoid rock in a greenstone, and not seldom of a peridotite 

 in a basalt. Hence, either the heavier rock, as a result of differ- 

 entiation, must sometimes rise (perhaps in the direction of cooling) 

 sometimes fall (perhaps in consequence of gravitation), or the one 

 rock, whatever it may be, in being squeezed upward or outward 

 from its original position, must be forced through the other. But 

 how and where differentiation has acted, whether by slow separation 

 and concentration in one and the same mass of magma, not long 

 before it began to move upward, or whether in the outer envelope 

 of the originally molten globe, we have no means of determining. 



Discussion. 



The Peesident said that the Fellows had the pleasure of listen- 

 ing to the Author dealing at one and the same time with two of 

 the subjects which he had made his own — the detailed geology of 

 Alpine regions and the igneous nature of serpentine. As respects 

 the Author's observations and conclusions on this interesting case, 

 they greatly strengthened the theory of those who held that such 

 masses of magnetic iron and the igneous rock now associated with 

 them had a common origin. We ought not, however, in fairness to 

 forget that many, probably the majority, of such masses of iron 

 found associated with basic igneous rocks under somewhat similar 

 conditions to those described, were met with in metamorphic rocks 

 lying, as it were, in the bared roots of greatly compressed and denuded 

 mountain-ranges. There was therefore a simpler hypothesis ex- 

 planatory of this association : namely, that many of these masses of 

 iron might be merely relics of ancient iron ore-deposits originally of 

 sedimentary origin, or deposited from solution, lying preserved in 

 pinched-in synclines and the like, and which had been intruded 

 upon and partly absorbed by igneous injections of much later 

 geological date. 



1 Zeitschr. fur prakt. Geol. vol. i (1893) p. 8. 



2 See summary of Prof. Vogt's work on the iron-ores of Norway and Sweden 

 (by J. J. H. T.), Geol. Mag. 1892, p. 82. [Since this paper was written my 

 attention has been directed to a most valuable and suggestive paper by Prof. 

 Vogt on ' Problems in the Geology of Ore-Deposits,' published, with contri- 

 butions from Messrs. J. F. Kemp & T. A. Packard, in Trans. Amer. Inst. 

 Min. Eng. vol. xxxi (1902) p. 125. As I could not obtain a sight of it till 

 this sheet was passing through the presF, I can do no more than say that 

 the case at Cogne is not cited, but would not, I think, be really adverse to 

 his views.] 



