34G RECORD OF SCIENCE FOR 1887 AND 1888. 



Cross, Whitman Ou some eruptive rocks from Custer Couuty, Colorado. Proc. 

 Colo. Sci. Soc, 1887, pp. 228-250. 



The rocks described are, (1) rhyolites, with primary corroded garuets ; (2) 

 trachytes, apparently allied to the so-called sauidiu-oligoclase trachytes of the 

 Siebeugebirge in Germany; (3) syenites; (4) peridotites, containing essential 

 hornblende and hypersthene, with accessory biotite, plagioclase, apatite, pyrrho- 

 tite, and sillimanite ; (f)) augite diorite, containing olivine; (6) sanidin bearing 

 audesite, in which the oligoclase crystals are nearly always surrounded by a zone 

 of orthoclase. 



Dalmer, Karl. Die Quartztrachyto von Campiglia nnd deren Beziehnngen zn 

 granitporphyrartigen nnd granitischen Gesteineu. Neues Jahrb, Min., Geol., 

 . etc., 1887, II Band, p. 20C. 



Derby, Orville A. On nepheline rocks in Brazil, with special reference to the as- 

 sociation of phonolite and foyaite. Quar. Jour. Geol. Soc, No. 171, August, 

 1887, vol. XLiii, p. 457. 



Describes the geological occurrence aud, to a certain extent, the lithologieal 

 characters of some peculiarly interesting nepheline and lencito rocks in the prov- 

 inces of Rio de Janeiro, Silo Paulo, and Minas-Geraes, Brazil. The more striking 

 features of the paper are the conclusions reached regarding the relations of the 

 phonolites and foyaites (eheolite syenite), the phonolite not only showiug in- 

 clusions of foyaite, but also the foyaite containing inclusions of phonolite, all 

 appearances indicating that they are both portions of the same magma ; that, in 

 short, the phonolite occurs as a peripheral facies of the foj'aite. A second re- 

 markable feature is the occurrence of leucite in rocks of undoubted paleozoic age. 

 The full significance of these discoveries may be best comprehended by those 

 not specialists in this lino of work if it be stated that the eheolite syenites are 

 deep-seated or plutonic rocks of paleozoic age, and of which the phonolites have 

 been considered the etfusive tertiary or post-tertiary equivalents. Moreover the 

 mineral leucite np to this time has been fouud as a constituent only of post-ter- 

 tiary lavas. The two discoveries, it will be observed, having a vei'y inijioriant 

 bearing upon the subject of rock history and classification, aud bringing once 

 more proof of the utter impossibility of relying upon mineral composition or 

 structure as a guide to geological age. The conclusions reached by Dr. Derby 

 may be best understood by quoting the author's exact words. He feels convinced 

 of, (1) the substantial identity as regards mode of occurrence and geological age 

 of the Caldas phonolites and foyaites ; (2) the connection of the latter through 

 the phonolites with a typical volcanic series containing both deep-seated and 

 aerial types of deposits; (3) the equal, if not greater, antiquity of the leucite 

 rocks as compared with the nepheline rocks, whether felsitic as phonolite, or 

 granitic as foyaite; and (4) the probable paleozoic age of the whole eruptive se- 

 ries. 



DiLLER, J. S., and George F. Kunz. Is there a diamond field in Kentucky? Sci- 

 ence, September, 1887, vol. x, p. 140. 



Elsdek, J.Vincent. Notes on the Igneous Rocks of the Lleyn Promontory. Geol. 

 Mag., July, 1888, p. 303. 



FouQUE, M. Snr les nodules de la grannlite de Ghistorrai pr6s Fonni (Sardaignej. 

 Bull. Soc. Fran^-aise Min^ralogie, February, 1887, vol. x, p. 57. 



The nodules occur in a grannlite consisting of quartz, orthoclase, oligoclase, 

 and both white aud black mica. They are rounded in outline aud consist of an 

 irregular nucleus of the same composition and structure as the inclosing rock 

 surrounded by a shell composed of concentric layers of albite and biotite. 



Petrographie de I'H^rault. Les porphyrites de Gabian. Note de MM. P. 



De Rouville et Auguste Dilage, presented bj' M. Fouque. Comptes Rendus, 

 October 22, 1888, p. ()6.i. 



Fox, Howard, and Alex. Somervail. Ou the occurrence of Porphyritic Structure 

 iu some rocks of the Lizard district. Geol. Mag., February, 1888, p. 75. 



