Geology and Natural History. 85 



and horizontal sheets of a dark colored, noncrystalline variety 

 of peridotite are found in the northern part of the area. 



The chief economic mineral of the district is fluorite, but in 

 places barite, galena, sphalerite and smithsonite have been 

 mined. These minerals occur in one of three ways : (1) Fissure 

 veins where the deposits fill fissures due to faulting ; (2) ores 

 cementing breccias which have been caused by the shattering of 

 the rock in a fault zone ; (3) metasomatic replacement of lime- 

 stone by zinc minerals. The first of these types is the most pro- 

 ductive. The source of the ore minerals is thought to have been 

 one or another of the limestone formations, the mineral material 

 having been transported and deposited in its present positions 

 through the agency of underground waters. 



The area is considered to form a minor division of the lead 

 and zinc districts of the Mississippi Valley but differs from the 

 others. in these respects: (1) In the presence of basic igneous 

 dikes ; (2) in the constant association of the lead and zinc ores 

 with fluorite, the latter occurring in well-defined fissure veins ; 

 (3) in the common occurrence of sphalerite in fine grains, largely 

 as a metasomatic replacement of the limestone in or adjacent to 

 the fissure veins. w. e. e. 



5. Die chemische Beschaffenheit von Erupting esteinen Finn- 

 lands unci cler Halbinsel Kola im Lichte des neuen amerilcanischen 

 Systemes ; von V. Hackman, Bull. Com. geol. de Finland No. 

 15, 1905, 8°, pp. 143. — In this work the author has collected all 

 the analyses of igneous rocks of Finland and the Kola peninsula 

 which have been made, many of them heretofore unpublished. 

 These are presented in tabulated form accompanied by their 

 calculated norms and classification according to the new Ameri- 

 can quantitative system for the classification of igneous rocks. 

 Collected into convenient shape these analyses will be a useful 

 addition to the library of every working petrologist. 



In his introductory chapter the author has much to say in 

 praise of the new system ; he doubts, however, whether it can 

 wholly replace the older one and suggests that the two should be 

 used together, each supplementing the other, the older being 

 modified to make it as quantitative as possible. l. v. p. 



6. Preliminary Announcement Concerning a New Mercury 

 Mineral from Terlingua, Texas ; by W. F. Hillebeand. — The 

 mercury minerals of the Terlingua District, Texas, are noted for 

 the unusual composition of several of their number. Besides cin- 

 nabar, calomel, and mercuric oxide, two oxychlorides, eglestonite 

 and terlinguaite, have been described in detail by Prof. A. J. 

 Moses (this Journal, xvi, 253, 1903), and a third, as yet unnamed, 

 has been provisionally identified by him as likewise an oxychlor- 

 ide. This last, the No. 5 of Prof. Moses, seems to be the chief 

 mineral on a number of specimens from the Terlingua District 

 lately received for identification from Mr. H. W. Turner. Its 

 examination reveals a composition most singular and apparently 

 representative of a class of compounds hitherto unknown in na- 



