Geology and Mineralogy. 429 



indicate the existence of a ventral plate. The fossil which he 

 described as P. bitruncata is maintained to be the Scaphaspid 

 plate of P. Americana." The genus is comj)ared with other 

 Pteraspid genera, and a restoration in accordance with his con- 

 clusions is given. — Ann. Mag. Nat. Hist., Oct. 1892, 334. 



6. Devonian fossils from the Islands and vicinity of Lakes 

 Manitoba and Winn epego sis, by J. F. Whiteaves, Canada 

 Geological Survey. — Mr. Whiteaves enumerates and describes a 

 large number of Devonian fossils from North-Central America 

 and illustrates them with many lithographic plates. The species 

 are in part identical with those of the United States. But a con- 

 siderable number are new; and they are of unusual interest also 

 " on account of the close relations brought out in many respects 

 between the fauna of these rocks and that of the Devonian rocks 

 of Europe." The collections were made by Mr. Tyrrell and the 

 author of the papers, and the localities are laid down on Mr. 

 Tyrrell's "geological map of Northwestern Manitoba, and por- 

 tions of the districts of Assiniboia and Saskatchewan," recently 

 published by the Canadian Survey. 



7. J. P. Iddings: "The Eruptive Rocks of Electric Peak 

 and Sepulchre Mt., Yelloiostone Nat. Park." Annual Report 

 TJ. S. Geolog. Survey, Vol. Nil. — The writer presents the result 



of his studies on groups of igneous rocks occurring in the north- 

 west corner of the Park. At Electric Peak occurs a stock of 

 diorite accompanied by a great number of dikes and of sheets 

 extensively intruded into Cretaceous strata. These rocks are 

 described in considerable petrographical detail with tables of 

 variation in structure and in chemical and mineralogical composi- 

 tion. From this it is shown that the variations in all directions 

 are most gradual and transitional and that it is impossible to dis- 

 tinguish sharply differentiated types. The rocks of Sepulchre 

 Mountain, a series of andesitic dikes cutting breccias, are treated 

 with like results and the relationship of the two occurrences 

 shown. Then follows a discussion of the bearing of the observed 

 facts on theoretical petrography: the writer establishes that the 

 same magma under differing physical conditions produce rocks 

 mineralogically different. In conclusion the subject of classifica- 

 tion is touched upon and the writer expresses himself in favor of 

 a system based on crystalline structure. The paper is ably 

 written and a most important contribution to petrographical 

 literature. l. v. p. 



8. A. Sauer : (Mittheihingen der Grossh. Badischen Landesan- 

 stalt. II. Rd.) — In a petrographical and geological study of 

 " The Granite of Durbach " the author describes a peculiar 

 syenite of lamprophyric character which surrounds the granite 

 as an outer zone and to which he gives the name of Durbachite. 

 Particularly interesting are the author's researches on the chem- 

 ical composition of the hornblende of this syenite. This obtained 

 in a state of great purity and freshness yielded 2*72 per cent of 

 water by the Sipocz-Ludwig method, although over the blastlamp 



