PETROLOGY. 223 



Ward, J. C. Notes on the Comparative Microscopic Rock- 

 Structure of some Ancient and Modern Volcanic Kocks. Quart, 

 Journ. Geol. Soc. vol. xxxi. pp. 388-422, pis. xvii., xviii. 

 Part 1 gives an account of the literature of the subject ; part 2 

 describes some modern volcanic rocks from Naples and Vesuvius ; 

 part 3 describes the volcanic rocks of Wales ; part 4 those of Cumber- 

 land. The general results, especially of parts 3 and 4, are: — 1. The 

 microscopic examination of rocks teaches us much of the conditions 

 under which volcanic rocks originated ; 2. The older volcanic rocks 

 are intensely altered, their original structure in some cases being pro- 

 bably obliterated ; 3. The Silurian lavas of Wales belong to the fel- 

 stone (= modern trachytic) group ; 4. The Silurian lavas of Cumber- 

 land belong to the basaltic group, or stand somewhere between it and 

 that of the felstones ; 5. In Wales and Cumberland felspathic ashes 

 have been metamorphosed into felstone-like rocks ; 6. Neither the 

 inspection of hand-specimens nor the microscopic examination of 

 slices would in all cases enable us to discriminate between trap and 

 altered ash-rocks ; but these methods, and chemical analysis, must be 

 accompanied often by a detailed survey of the rocks, the various beds 

 being traced out, aixd their weathered surfaces particularly noticed. 



W. T. 



Warden, C. J. H. Analysis of Mud taken at low water from the 

 Mer Rouge, Mauritius. Chem. Neivs, vol. xxxi. p. 274. 



Weigand, Bruno. Die Serpentine der Vogesen. [Serpentines of 

 the Vosges.] Min. Mitt. Heft iii. pp. 183-206, 2 figs. 



Sketches the history of opinion on the origin of seri)entine. The 

 rock occurs in three districts in the Vosges, of which two are on the 

 German side, in Upper Alsace, at the Bluttenberg or Bressoir in the 

 N., and at the Amarinerthal in the S. These two occurrences are 

 described. The writer concludes that not only can olivine be altered 

 into seri)entine, but other magnesian silicates, poor in alumina, as 

 bronzite and hornblende, can also give rise to this stable hydrate as a 

 product of their decomposition. F. W. R. 



Wichmann, Dr. A. [Nepheline-basalt from the Sandwich Islands.] 

 N. Jahrb. Heft ii. pp. 172, 173. 



Describes the microscopic structure of a basalt brought to Hamburg 

 as ballast from Oahu in the Sandwich Islands. It contains beautifully 

 formed crystals of nepheline, with melilite, nosean, hauyne, and 

 olivine. F. W. R. 



[Melaphyre of the Plauen'sche Grund.] N. Jahrb. Heft vi. 



pp. 623, 624. 



Haarmann has suggested that the so-called melaphyre of the 

 riauen'sche Grund, near Dresden, is properly a minette. The writer 

 objects, maintaining that it is an augite-and-plagioclaso rock with 

 olivine, thus quite different from minette. F. W. R. 



