PETROLOGY. 221 



hygroscopic water diminishes, while the proportion of so-called fixed 

 carbon as well as the capacity for making good coke increases, with 

 the age of the seams, those contained in the lower measures being the 

 most valuable gas and coking coals. The classification proposed by 

 Hilt and Gruner, where the yield of coke is taken as the measure of 

 the other qualities of a coal, is shown not to be applicable to the dis- 

 trict under review. The second part treats of the physical structure of 

 the coals and their relative coking quality, concluding with speculations 

 on the nature of the changes undergone by woody tissue in its con- 

 version into coal. H. B. 



Schweitzer, Prof. P. On the Composition of Coal and on the 

 methods of arriving at it, with deductions and remarks on Coal in 

 general; illustrated on a sample of Coal from the Lower Coal 

 Series of Missouri, and on the Water Supply of Columbia, Mis- 

 souri. Contributed from the Laboratory of the University of 

 Missouri, pp. 156-193, published in the Catalogue of the Univer- 

 sity, Jefferson City. 



Skey, William. Notes on the Formation and Constitution of Tor- 

 banite. Chem. News^ vol. xxxi. pp. 16, 17. 



Experiments show that clay can absorb the colouring-matter of 

 petroleum passing through it. If the process be carried on to a small 

 extent we obtain only a feebly bituminous clay ; but if carried to 

 saturation of the clay the resulting substance resembles torbanite. The 

 absorption is not of a mechanical but chemical nature. The author 

 believes that torbanite is a combination of a bituminous substance with 

 the clay ; therefore not a coal, but probably a chemical combination of 

 an acid hydrocarbon with silicate of alumina. F. W. R. 



Snelus, G. J. Fire-Clay and other Refractory Materials. Iron and 



Steel Institute. Irorij vol. vi. pp. 422, 423. 

 Analyses given of clays, ganuister, &c. 



Streng, A. [Porphyrite of Ilfeld]. N. Jahrh. Heft vi. p. 624. 



This rock consists of a compact matrix composed of orthoclase, oligo- 

 clase, hornblende, quartz, magnetite, and apatite, with porphyritic 

 enclosures of triclinic felspar, hornblende, titanic iron, magnetite, and 

 quartz, sometimes with graphite, garnet, &c. F. W. R. 



. Mikroskopische Untorsuchung der Porphyrite von Ilfeld. 



[Porphyrite of Ilfeld.] N. Jahrh. Heft viii. pp. 785-811 ; wood- 

 cut. 

 The porphyrite of Ilfeld consists of an apparently compact matrix of 

 orthoclase, lime-soda felspar, honiblende, quartz, magnetite, apatite, 

 and sometimes graphite, perhaps also titanic iron-ore. In this matrix 

 arc pori)byritically embedded crystals of lime-soda fela])ar, hornblende, 

 quartz, and perhaps graphite and magnetite. The Ilfeld rock thus 



