154 FULLER AND CLAPP — MARL-LOESS OF LOWER WABASH VALLEY 



15-minute quadrangles in southern Indiana and Illinois for the U. S. 

 Geological Survey. Most of the evidence was obtained from the Mount 

 Carmel, Princeton, and New Harmon}^ quadrangles, or those crossed by 

 the Wabash river, though a number of minor, yet important features 

 bearing on the loess problem were noted in the Haubstadt, Boonville, 

 and Petersburg quadrangles to the eastward (figure 1). With the excep- 

 tion of the dunes of probable late Winconsin stage, occurring along 

 the border of the Wabash valley, and the recent fiood-plain deposits 

 bordering all but the smallest streams, the entire surface of these quad- 

 rangles is covered with a mantle of fine silts. Up to the present time no 

 attempts to difi'erentiate these silts have been made, the whole mantle 

 apparently being regarded as a unit and designated as loess.^ The de- 

 tailed field work of the writers, during which all the roads and many 

 of the intervening areas in the region along the Wabash river were cov- 

 ered, brought to light sufficient diff'erences to warrant, it is believed, the 

 diff'erentiation of the surface silts of the region into two distinct physical 

 types. The first of these types includes the thick, yellowish, and highly 

 calcareous silts along the immediate borders of the Wabash valley which 

 are believed to be of aqueous origin. For purposes of discrimination in 

 the following discussion it is designated as marl-loess. The second t3'pe 

 embraces the more clayey and oxidized silts forming the mantle over 

 portions of the surface more remote from the river, and as a type is 

 known as common loess. Although there are no reliable criteria for the 

 subdivision of the latter by its ph3"sical or chemical characters, there 

 are several lines of evidence which will be discussed later which seem 

 to indicate that it is not of the same origin throughout, but that its 

 accumulation, though in the main eolian, was in part aqueous. In the 

 following discussion the term common loess is used, as indicated above, 

 to designate a physical t3^pe without implied mode of origin. The terms 

 aqueous division and eolian division are used to characterize the sub- 

 divisions of the common loess. 



Comparison of the Common and Marl-loess Types 



common loess 



Description. — The common loess of southwestern Indiana is an excep- 

 tionally fine silt, usually buff' or brown in color, which, as a whole, mantles 



* See D. D. Owen, in Report of the Geol. Survey of Wisconsin, Iowa, and Minnesota, 1852, p. 132 ; 

 John Collet, in Report of the Indiana Geol. Survey, vol. 13, pp. 47-48 ; G. F. Wright, U. S. Geol. 

 Survey, Bull. 58, p. 70; T. C. Chamberlin and R. D. Salisburj', Am. Jour. Sci., 3d series, vol. 41, 

 p. 361 ; T. C. Chamberlin, Jour. Geol., vol. 5, p. 795, and Frank Leverett, U. S. Geol. Survey, Mono- 

 graph 38, p. 156. Owen in the Second Report of the Indiana Geol. Survey, 18.38, describes an occur- 

 ence of marl "four miles north of New Harmony," but does not discuss its relations or mode of 

 occurrence. 



