458 W. J. McGee — Three Formations of 



either flood stage, and read from the precipitates a record of 

 (1) flooded condition of the basin without free drainage, (2) 

 shrinking and concentration of the waters and precipitation of 

 lithoid tufa (which was overlooked by King), (3) spasmodic 

 reflooding of the basin and successive precipitation of (a) the 

 mineral now pseudomorphosed into thinolite and (b) dendritic 

 tufa (also overlooked by King), and (4) shrinking of the waters 

 to below present level, followed by a slight re-advance.* This 

 sequence of events is quite inconsistent with that deduced by 

 King, and it thus appears that the coincidence in interpretation 

 of the Lahontan precipitates by King and Russell respectively 

 is no more than curiously fortuitous, and adds nothing to the 

 weight of opinion of either investigator nor to the reliability 

 of the history inferred from other phenomena. But there is a 

 definite sequence of deposits in the Great Basin indicating a 

 definite sequence of events (and the testimony of these deposits 

 is corroborated by the shore-lines and by the precipitate as 

 interpreted by Russell), viz : (1) basal gravels, representing 

 long-continued arid climate; (2) lower lacustral beds; (3) 

 medial gravels ; (4) upper lacustral beds ; and (5) recent 

 gravels, etc. ; and the two lacustral periods are correlated by 

 Gilbert and Russell with two vaguely defined periods of 

 northern glaciation.f 



A fairly complete sequence of glacial and aqueo-glacial 

 deposits in Iowa and northern Missouri affords a record of the 

 early Quaternary history of the central Mississippi valley. It 

 was pointed out by the writer in 1878, and again in 1879, that 

 the bipartition of the glacial deposits and the intercalation of 

 a forest bed within them in Iowa indicate two ice invasions 

 separated by a long interglacial period ;;{: in 1880 it was made 

 known that the lower glacial deposit (or till) graduates upward 

 into a series of stratified clays and extends much farther south- 

 ward than the upper, which is associated with or graduates 

 upward into loess ;§ in 1 882 it was shown that the loess is 

 overlain by a third drift sheet, probably connected with the 

 terminal moraine ;|| and recent investigations have shown that 

 the stratified upper member of the lower till (locally known as 

 "■gumbo") not only bears unmistakable structural evidence of 

 aqueous deposition but exhibits in its topographic configura- 

 tion evidence of submergence of an extended area in .Nebraska, 



* Op. cit. (2), 236. 



f While the lacustral deposits of the Great Basiu are regarded as Quaternary 

 by every stratigraphist and physical geologist who has investigated the subject, 

 they have' been referred to the Tertiary upon paleontologic grounds by Cope (Am. 

 Naturalist, vol. xxi, 1887, 458-9) and perhaps others. 



% This Jour., Ill, vol. xv, 1878, 339-41; Proc. Am. Ass'n for Adv. of Sci., 

 vol. xxvii, 1878, 198-231 ; Geol. Magazine, N. S., vol. vi, 1879, 353-361, 412-420. 



§ Trans. Iowa Hort. Society, 1880. 



|| This Journal, III, vol. xxiv, 1882, 222. 



