ology and Natural History, 819 



but (fu feldspar still Bound, The decayed rook crumbles to the 

 same kind ol Band as that out of which the Triassio quartz-fold- 

 spar Baodstone (arkose) of the region was made. 



With regard to the red color o( the Triassio Bandstone, respect- 

 ing which tlic writer is quoted, but misunderstandingly, the fad 

 has been before him that the Bands made by decomposition in the 

 region are not incrnsted with red oxide of iron (hematite), but 

 with brown (limonite) ; and, accordingly, the condition under 

 which the color became red has been regarded as a subsequent 

 one, as that attending the wide-spread consolidation of the rock. 

 It is explained thus in his Manual of Geology, on page 7<'>l 

 (edition of 18S0) : "A region invaded by trap eruptions is often 

 also, as a consequent or concurrent fact, a region of steaming fis- 

 sures and of hot springs, conveying the heated moisture widely 

 through the strata of the region; and thus the sand-beds of the 

 same Mesozoic formations in the Connecticut valley were gen- 

 erally reddened as well as consolidated — the oxidation of iron, 

 when taking place through the agency of hot waters producing 

 the anhydrous red oxide." Under such conditions any limonite 

 present about the grains of the loose sand-beds would have been 

 made red. The sandstone wall-rock of dikes is often of a light 

 gray color, instead of red, because the iron is put by the heat 

 into a silicate condition. Familiar blowpipe experiments illus- 

 trate both effects. A touch of the blowpipe-flame will redden 

 most sandstones not already red, from the olive-colored building- 

 stone of New Brunswick to varieties of the white of Ohio ; 

 proving, as the writer has stated (1873, 1880), that many great 

 sandstone formations would redden in the early stages of oro- 

 graphic movements, or from heat supplied in any other way. 

 The firm consolidation of a sandstone is, in general, evidence 

 that the needed heat has been present. J. o. d. 



-. Geologie de V Ancienne Columbie Bolivarienne, Venezuela, 

 Xouvelle Grenade et Ecuador; par Hermann Karsten, 62 pp. 

 4to, with a colored map, two plates of profiles and sections and 

 six plates of fossils. Berlin, 1886 (R. Friedlander & Sohn). — 

 This valuable memoir, on the geology of a large section of 

 northern South America, commences with remarks on the general 

 features of the country under consideration, and a history of 

 previous investigations from the time of Humboldt, ninety years 

 since. The author began his studies of South America in Vene- 

 zuela and carried them on during the years 1844-47, 1840-56, 

 and his results were the subject of publications between the 

 years 1849 to 1860 and later. The new volume is a collection of 

 all his reports, together with a review of the work of other geo- 

 logists in the region. The careful descriptions and the colored 

 geological map, together with the paleontological plates and the 

 observations on the volcanoes of the Andes, makes the work one 

 of special importance. The map covers the part of South 

 America west of the meridian of 5$± west and north of the 

 parallel of 5° south. A large area bounded on the north, w 



