36 SCIENCE PROGRESS 



(2) Load-Contact Metamorphism (combination of load 

 and magmatic influences). 



In the same publication W. J. Miller has essayed a classifica- 

 tion of metamorphic rocks (ibid. 451-62). He divides them up 

 into the following groups : (1) Meta-igneous rocks ; (2) Meta- 

 sedimentary Rocks ; (3) Injection foliates ; (4) Foliates of 

 unknown origin ; (5) Saprolites (products of rock decay). 

 The first two groups are then subdivided into Foliates and Non- 

 foliates, and finally according to composition. The remaining 

 three divisions are simply classified according to composition. 



A. L. Hall gives an interesting description of the contact 

 belt of the Older Granite, in the Barberton District and Northern 

 Swaziland (Transvaal) (Trans. Geol. Soc. South Africa, 191 8, 

 20, 1-36). The commonest rock is andalusite-slate with or 

 without ottrelite ; then comes chiastolite-slate, biotite-hornfels, 

 and altered quartzite. The average width of the contact aureole 

 is about three miles, which contrasts remarkably with the twelve- 

 mile aureole of the Bushveld complex. The difference is 

 ascribed partly to different modes of intrusion, partly to 

 differences in the rocks involved ; but probably depends 

 mainly on the greater abundance of mineralising agents in the 

 Bushveld complex, which is further attested, by the wide 

 distribution of tin ore within or near it. 



Teall, Sir J. J. H., Dynamic Metamorphism, a Review, 

 mainly Personal, Proc. Geol. Assoc. 1918, 29, 1-15. 



Cox, A. H., Notes on Some South Staffordshire Fireclays 

 and their Behaviour on Ignition, Geol. Mag. 191 8, 5, 56-63. 



In a paper entitled " A Contribution to the Micropetrology 

 of Coal," G. Hickling makes the interesting observation that the 

 colour-density of coal (observed in thin section or in the streak) 

 increases regularly with the carbon content, and he suggests 

 that with standardised streak-plates it might be possible to 

 determine carbon percentages by this method to well within 

 5 per cent. He also shows that all coals exhibit at least four 

 elements : lignitoid vegetable tissue ; the cuticles from the 

 epidermis of stems and leaves ; hard coats of the spores of 

 plants ; and finally a dark, structureless substance consisting 

 of minutely-comminuted debris, which forms a matrix for the 

 other constituents. 



The investigation of the textures of dolomitic limestones 



