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LXI. Notices respecting New jBoofa 



Chemical and Physical Studies in the Metamorphism of Rocks, based 

 on a Thesis (with Appendices) ivritten for the Doctorate in Science 

 in the University of London. By A. Ikvim}, JD.Sc, B.A., F.G.S. 

 8vo. 138 pages. Longmans & Co., London. 



T> OCK-METAMOBPHISM, considered from the chemical and 

 ■*-*' physical side, introduces the subject, which, after a definition 

 of " metamorphism," as here meaning " only changes in the internal 

 structure of rock-masses," is divided into three divisions — paramor- 

 phism, metatropy, and metataxis. The first refers to atomic, that 

 is chemical, changes ; the second to molecular, that is physical, 

 changes ; and the third to mechanical conditions. In one case the 

 process is, as it were, the dissociation of a molecule into atoms ; in 

 the next, the breaking up of a solid into a liquid and then into a 

 gas, the cohesion of the mass being gradually overcome until it 

 becomes divided into molecules ; in the third case, we have molar 

 division, by pressure, percussion, or grinding. Such a change in a 

 rock as is due to the introduction of a new, or the removal of an 

 old mineral, and referred by many to metamorphism, is here 

 separately noticed as hyperphoria change. 



I. Paramorphism, or mineral change, divides itself into — 1. 

 Primary paramorphism (Genesis of Bocks), which leads to the 

 recognition of a universal glowing magma at an early stage of the 

 Earth's Evolution : — 2. Secondary paramorphism, brought about by 

 the action of saline (marine) waters in producing secondary 

 minerals, derived from the primary minerals of the rock and not 

 altering the composition of the rock when tried by bulk-analysis. 

 Examples referred to are separation-products in slates and shales, 

 - — siliceous cements in volcanic tuffs and sarsen stones, — calcite in 

 some igneous rocks, — quartz in the quartz-porphyries of Bozen, — 

 facts published by Judd, Allport, Bonney, Becker, and others. 



II. Metatropy is defined and illustrated. The conversion of 

 coal into anthracite and graphite, with a slight change in chemical 

 composition, may be metatropic ; the formation of palagonite and 

 hydrotachylite from the glass of basalts by hydration, — the change 

 of anhydrite into gypsum, of arragonite into calcite by dry heat, 

 and of calcite into arragonite by solution and heat, — the results 

 of contact metamorphism by heat, as some grauwackes and shales 

 into hornstone and porcellanite, — of coal into coke, — sandstone 

 into quartzite, — and limestone into marble, are metatropic. Poly- 

 morphism is included in metatropy; and this variation of crys- 

 talline form is brought about by: — 1. Temperature, as with carbonate 

 of lime ; 2. Molecular water, as with native hydrates of alumina 

 and in some silicates of copper ; 3. An accessory mineral, as with 

 carbonate of lime tainted with some carbonates of the alkaline 

 earths ; and here the author suggests that these may have the 

 rhombic system of arragonite rather than the hexagonal for their 



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