74 BIBLIOGRAPHY AND INDEX OF N. A. GEOLOGY, Tbull. 146. 
469 Tilton (J. L.). On the southwestern part of the Boston Basin 
[Massachusetts]. 
Boston Soc. Nat. Hist., Proc, vol. xxvi, pp. 500-505, with map. 
Describes the general character of the rocks, with a discussion of 
special parts of the boundary between the granite and basin rocks. 
470 Geological section along Middle River, in central Iowa. 
Iowa Geol. Surv., vol. iii, 2d Ann. Kept., pp. 137-146. 
Gives a cross section of the region and the vertical section of the Car- 
boniferous rocks at various localities. Discusses the subdivision of the 
Iowa Coal Measures into upper and lower divisions. 
471 Todd (J. E.). Inequalities in the old Paleozoic sea bottom. 
Am. Geol., vol. xv, p. 64 (£ p.) (correspondence). 
Gives the depths at which crystalline rocks were struck in well borings 
at various localities in Iowa and Nebraska. 
472 Volcanic ash bed near Omaha [Nebr.]. 
Am. Geol., vol. xv, p. 130 (•£ p.) (correspondence). 
Describes briefly an occurrence of a volcanic ash bed in the bluffs of 
the Missouri Eiver near Omaha, Nebr. 
473 Recent geological work in South Dakota. 
Am. Geol., vol. xvi, p. 202 (correspondence). 
Gives a brief statement of some of tbe recent results obtained by two 
parties sent into the field by the School of Mines of South Dakota. 
474 and Bain (H. Foster). Interloessial till near Sioux City, 
Iowa. 
Iowa Acad. Sci., Proc, vol. ii, pp. 20-23, pi. 1. 
Describes the outcrop of the till in the banks of the Big Sioux Eiver. 
Discusses its origin. 
475 Turner (Henry W.). The age and succession of the igneous rocks 
of the Sierra Nevada. 
Jour, of Geol., vol. iii, pp. 385-414, with map. 
Describes the topographic and general geologic features of the Sierra 
Nevada range and the character, age, and succession of the igneous 
rocks. Includes chemical analyses of some of the j)re-Tertiary and Ter- 
tiary igneous rocks and a geologic map of tbe region. 
476 Auriferous gravels of the Sierra Nevada. 
Am. Geol., vol. xv, pp. 371-379. 
Reviews the paleontologic evidence as to the age of the two groiips 
into which the auriferous gravels are divided. Presents a report by 
F. H. Knowlton on the fossil plants collected at certain localities in 
California. 
477 Further notes on the gold ores of California. 
Am. Jour. Sci., 3d ser., vol. xlix, pp. 374-380. 
Describes the occurrence of gold iu barite, gold associated with talc- 
schists, and the occurrence of gold-quartz veins in Tertiary rocks in 
California. 
Describes the occurrence and chemical composition of mariposite .and 
the occurrence of tetrahedrite iu quartz veins. 
