334 Tiie American Oeologist. November, is97 
They are photolithographed and printed by Giescke and Devrieut, 
Leipzig, but the work issues from John G. Stomler and Co., Amster- 
dam, published by order of the governor-general of the Dutch Indies. 
N. H. w. 
Geology of Polk County [lotva]. By H. F. Bain. (Iowa Geol. Sur- 
vey, vol. 7, pp. 263-412, pis. 7 9, 2 maps, 1897.) This county, situated 
near the centre of the state, is of special interest in that it contains the 
apex of the Des Moines lobe of the latest drift sheet; and. moreover, here 
were obtained some of the important data which have Vjeen used re- 
cently by the members of the Iowa survey, especially Messrs. Calvin and 
Bain, in their separation and classification of the different drift sheets 
of the state. At Des Moines, in the southern half of the county, the 
Kanaan drift, the lowan loess and the Wisconsin drift are all well de- 
veloped and can be easily separated. There are also some facts indicat- 
ing the possible presence of a pre-Kansan drift. The three parts of the 
Pleistocene above mentioned can be separated by three important fea- 
tures; (1) by actual overlie, some sections showing the three present in 
ascendiag order as given above: (2) by difference in composition and 
physical characters: (3) by difference in surface contour. The streams 
flowing in the older drift surface are approaching maturity, the divides 
are well marked and the country is well drained, while in the newer 
drift the streams are young, the divides are not well marked and the 
country is poorly drained as shown by the numerous swales. The main 
drainage channels, of which the valley of the Des Moines river is the 
largest, are shown to have been preglacial, consistingof wide valleys ex- 
cavated in the Coal Measure strata and later filled in with drift which 
has not been entirely removed. 
The surface rocks below the drift all belong to the Des Moines stage 
of the Upper Carboniferous. They contain important beds of coal, Polk 
county being one of the foremost counties of the state as regards coal 
production. The clays, both Pleistocene and Carboniferous, but chief- 
ly the latter, are used extensively for manufacturing purposes, the most 
important products being, brick, paving brick and tile. The report is 
accompanied by two maps, one showing the Pleistocene and Recent and 
the other the pre-Pleistocene geology. u. s. g. 
Eine Torfmoor initersnchung aus devi nordliclien Nerike, vonRuTGER 
Sernander und Knut Kjellmark. (Geol. Inst. Upsala, No. 4, vol. it. 
pt. 2, 1895.) 
Une travaille arcMologique faife dans une tomhih-e au nord de la 
Ndricie, par Knut Kjellmark. (Geol. Inst. Upsala, No. 5, vol.iii, 1896.) 
Some interesting results of the study of peat bogs in Sweden have 
been made known within the last few years. 
A mong others is the determination of a series of climatic changes obser- 
ved through the sensitive barometer of plant distribution. The length 
of time has been sufBcient to allow of the development of varieties in 
some plants among which may be named the water chesnut [Trapa na- 
tans) which was an article of food with prehistoric man in Europe. 
