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



removed extensive accumulations which must have existed between the 

 " islands " and the highlands bordering the valley on the east. The 

 eastern borders of the marl-loess deposits east of the Wabash are marked 

 by important drainage lines, probably in part consequent upon the con- 

 structional forms resulting from the deposition of the marl-loess. 



Color. — In color the marl-loess varies from nearly white through a 

 light gray to a light buff. B}'' far the larger part, however, is character- 

 ized by a pale straw or yellowish color, which, with one exception (see 

 page 173), had no counterpart in the eolian loess of the region, and 

 which therefore affords a good general guide to its recognition. The 

 yellowish color, however, is generally found only in the main belt of 

 marl-loess bordering the Wabash valle3^ In the few remote and appar- 

 ently outlying deposits which have been recognized the color is usually 

 gray. The gray type is especially impervious to water, in some cases 

 remaining almost w^holly unoxidized and unleached even where within 

 3 or 4 feet from the surface. The 3"ellowish variety, on the other hand, 

 is more porous, and is generally slightly oxidized throughout, although 

 only the upper 2 or 3 feet exhibit the brown and reddish colors which 

 nearly everj^where characterize the common loess. This oxidation of 

 the surface of the marl loess occurs only when the latter is destitute of 

 the coating of loess of the ordinary t3^pe. It can usually be distinguished 

 from the ordinar}^ loess, which it strongly resembles, by its deeper red- 

 dish brown color and the presence of numerous fine, but rather stiff, clay 

 lumps such as frequently characterize the weathering of argillaceous 

 limestones. Neither the gray nor yellowish types, with the single ex- 

 ception noted on page 173, are ever typically developed above the 500- 

 foot contour. 



Composition. — The most conspicuous physical difference between the 

 marl-loess of the yellowish type and the ordinary loess is the greater 

 coarseness of the former. In fact, it might in some instances be termed 

 a fine sand rather than a clayey silt, the individual grains being dis- 

 tinctly visible in several cases. To the unaided eye the grains appear 

 to consist mainly of quartz, though in certain layers finely comminuted 

 shells compose a considerable portion of the material. 



In the following table analyses of the common and marl-loess types 

 are given for comparison. Number 1 is a sample of ordinary loess from 

 near Princeton, and was analyzed by Professor Robert Lyons for the 

 Indiana Geological Survey and published in the twentieth and twenty- 

 first annual reports. Number 2 is a sample of marl-loess from the land 

 of B. C. Macey ("4 miles north of New Harmony "), and was given in 

 D. D. Owen's report.^ The two are selected because they mark extremes 



*"A Geological Reconnaissance of the State of Indiana," pt. 2, 1838, p. 66. 



