Correspondence — Dr. H. J. Johnston- Lav is. 881 



Dr. G. T. Prior : Re-determination of Nickel in tlie Baroti and 

 Wittekrantz Meteorites. Precipitation with ammonia was found not 

 to separate iron from nickel completely, however often the operation 

 was repeated. Ke-determination showed that the proportion of iron 

 to nickel in the case of hoth the meteorites in question was nearer 

 6 : 1 than 10:1 as previously stated. — Dr. L. L. Fermor : Ice Crystals 

 fiom Switzerland. Last winter the surface of the snow in shady 

 situations near Zweisimmen and I>enk was often characterized by 

 a dense growth of hollow prisms formed of a thin shell of ice coiled 

 spirally parallel to the face of a hexagonal prism. — Dr. L. L. Fermor: 

 Hematite from the Kallidongri Manganese Mine, India. The crystals, 

 which had the habit of corundum and were marked with three sets of 

 striations due to twin lamellatiou parallel to 100, showed the forms 

 111 and 614 well developed, together with _100, 221, 28.28.13 

 (a new rhombohedron), 513, 715, and 101 less prominent. — 

 H. B. Cronshaw : A variety of Epidote from the Sudan. A mineral 

 discovered by Mr. G. W. Grabham in a pegmatite vein closely 

 resembles allanite in appearance, but is free from rare earths and 

 agrees in composition with epidote ; in its pleochroism and negative 

 sign it also resembles the latter, but has an abnormally low optic- 

 axial angle of about 54 degrees. In thin section it represents 

 a well-marked zonal sti'ucture. 



COE,I?,BS:E'OD^TIDE!ITCE. 



SATURATION OF MINERALS AND GENESIS OF IGNEOUS ROCKS. 



Sir, — The separation of the different mineral components of an 

 igneous rock is so complex a question that it requires a careful study 

 of each individual rock type, with every effort to follow tlie different 

 vicissitudes to which it has been subjected from its original state of 

 a homogeneous, vitreous paste, through its raagmatic differentiation 

 till its final cooling, not to speak of subsequent changes. In the vast 

 majority of somewhat ancient rocks that are only exposed by erosion 

 the time occupied by this may represent very considerable changes 

 subsequent to complete consolidation. 



I fully agree with Mr. A. Scott ^ in his protest against the 

 classification of rocks independent of their ' cooling history ', or, to 

 put it more correctlj', he agrees with me! The American classification 

 of rocks I look upon as many steps backwards by this introduction of 

 a cumbersome nomenclature and diagrams, interesting perhaps to the 

 chemists, but murderous to the true naturalist or geologist. It hides 

 the beautiful forms of geological phenomena under a gaudy patchwork 

 mantle of mostly untenable hypotheses spangled with fantastical 

 names. I say that Mr. A. Scott agrees with me, for, if he will 

 consult the papers quoted below,' he will find himself forestalled in 



^ See Geol. Mag., July, 1914, pp. 319-24. 



^ " Geology of Vesuvius and Monte Somma " : Q.J.G.S., vol. xl, pp. 35-119, 

 1884. "Some Speculations on the Phenomena suggested by a Geological 

 Study of Vesuvius and Monte Somma": Geol. Mag., Dec. Ill, Vol.11, 



