197 



PETROLOGY. 



AcHiARDi, Antonio d'. Sulla conversione di una roccia argillosa in 

 serpentino. [On the conversion of an argillaceous rock into ser- 

 pentine.] Boll. R. Com. geol. Ital. pp. 366-369, woodcut. 

 Note on a section near Vignalo, in the Province of Florence. An 

 altered rock, traversed by veins of steatite and dolomite, contains 

 nodules of serpentine coated with dolomite. These nodules may be 

 traced gradually through all the stages of argillaceous rock into serpen- 

 tine : the alumina replaced by magnesia has been separated as a white 

 substance of the appearance of halloysite. E. B. T. 



Allex, J. A. Metamorphic Products from the burning of Coal- 

 Beds of the Lignitic Tertiary in Dakota and Montana. Amer. 

 Journ. ser. 3, vol. viii. pp. 141, 142. 



Abstract of paper in Proc. Boston Soc. Nat. Hist. vol. xvi. 1874. 



Allport, S. On the Microscopic Structure and Composition of 

 British Carboniferous Dolerites. Quart. Journ. Geol. Soc. vol. xxx. 

 pp. 529-567 (2 plates). 



The paper is based upon an examination of specimens from fifty- 

 seven localities (Scotland, Ireland, Northumberland, and the Midland 

 counties). As regards terminology, the author proposes to include all 

 basic augitic rocks under the general name Dolerite, and to discon- 

 tinue the use of such terms as Melaphyre, Aphanite, Anamesite, Dia- 

 base, and Greenstone. As regards the age of the rocks described, they 

 are all supposed to be older than Permian. The minerals of which the 

 Dolerite are composed are classed under the heads of original and 

 secondary constituents : the latter (products of alteration) comprehend 

 chlorite, calcite, and quartz ; the former felspar, augite, magnetite, 

 olivine, apatite, and mica. These minerals are each noticed, and 

 then the Dolerites from the various localities are described. There are 

 some masses of trap in the Carboniferous rocks of Scotland not yet 

 examined. But all other basic rocks of tlie Carboniferous Series known 

 to the author belong to the augitic group, with only two exceptions — 

 the gabbro from Corstorphino Hill, Edinburgh, and the hornblendic 

 trap of the Warwickshire Coal-fields. W. T. 



. Note on the Phonolitc from the " Wolf Rock." Geol. Mag. 



dec. 2, vol. i. pp. 462, 463. 



In examining microscopic sections of this rock the author finds that 

 some of the crystals which he had taken for nepholine present the 

 physical characters of noscan. This mineral had not been previously 

 recognized in these islands. The '• Wolf Hock " appears to be a typi- 

 cal phouolite, consisting of nepheline, no8ean,8anidine, hornblende, and 

 magnetite. F. W. R. 



