52 BIBLIOGEAPHY OF NORTH AMERICAN GEOLOGY, [bull.203. 
422 Keyes (Charles R.). A depositional measure of unconformity. 
Geol. Soc. Am., Bull., vol. 12, pp. 173-196, pi. 19, 1901. 
Describes the development of the Carboniferous sediments in the Mis- 
sissippi Valley and Southwestern regions. 
423 Origin and classification of ore deposits. 
Am. Inst. Mg. Engrs., Trans., vol. 30, pp. 323-356, 1901. 
Discusses the nature of ore deposits, general methods of ore formation, 
the classification of ore deposits, and certain other phases of ore deposits. 
-424 - - Derivation of the terrestrial spheroid from the rhombic 
dodecahedron. 
Jour. Geol., vol. 9, pp. 244-249, 1901. 
Discusses Green's hypothesis of the tetrahedral form of the earth. 
425 - Composite genesis of the Arkansas Valley through the Ozark 
highlands. 
Jour. Geol., vol. 9, pp. 486-490, figs. 1-2, 1901. 
Discusses the evidences winch indicate that there lias been but one 
uplift in the region and that the river eroded its bed as fast as the strata 
were raised. 
426 -[Review of " Uintacrinus; its structure and relations by 
Frank Springer; " Oriskany fauna of Becraft Mountain" 
by rl. M. Clarke; and " Stratigraphical succession of the 
fossil floras of the Pottsville formation in the southern 
Anthracite coal field" by David White.] 
Join'. Geol., vol. 9, pp. 539-547, L901. 
427 — [Review of "Zinc and lead region of north Arkansas " by 
John C. 1> rainier.] 
Jour. Geol., vol. 9, pp. 634-636, 1901. 
428- - Ore formation on the hypothesis of concentration through 
surface decomposition. 
Am. Geol., vol. 27, pp. 355-362, L901. 
Discusses the evidence as to the derivation of the lead and zinc ores 
of the Ozark region and their bearing on the origin of ore deposits in 
general. 
4^1> - Nomenclature of the Cambrian formations of the St. Francois 
Mountains [Missouri]. 
Am. Geol., vol. 28, pp. 51-53, 1901. 
Discusses the validity of certain names applied to the Cambrian for- 
mations of the region. 
430 [Reviews of ''Paleozoic faunas of northern Arkansas " by 
H. S. Williams; -What is an Echinoderm?" by F. A. 
Bather; and u Structure and relations of Uintacrinus " Iry 
Frank Springer.] 
Am. Geol., vol. 28, pp. 254-260, 1901, 
