156 FULLER AND CLAPP — MARL-LOESS OF LOWER AVABASH VALLEY 



The common loess has not been found to carry fossils at any point in 

 the region examined ; nor does it contain pebbles except where the 

 sheet is so attenuated that roots penetrate to the till beneath, and on the 

 falling of the tree drag the pebbles upward into the loess. The common 

 loess of the region never presents definite evidences of stratification, 

 though an occasional indistinct bandinoj concentric with the surface and 

 made visible because of difi'erences in moisture absorption capacity of 

 the materials were noted. 



Distribution. — Along the borders of the east side of the Wabash valley, 

 loess of the common type is often absent, marl-loess frequently forming 

 the immediate face of the bluff's. This might naturally be attributed to 

 the action of aqueous erosion produced by the impingement of the river 

 during its meanderings subsequent to the deposition of the marl-loess, 

 but its frequent absence from the top for short distances back from the 

 edge of the bluff's calls for some other explanation. 



Though differentiated only with some difficulty from the marl-loess, 

 a thin coating of the common type usually appears to begin within a 

 quarter or half a mile of the edge and increases gradually in thickness 

 for several miles, probably reaching a maximum of 15 feet or more at a 

 distance of 6 or 7 miles, beyond which it slowly decreases, until at a 

 distance of 35 or 40 miles it has a thickness of only 2 or 3 feet, or pos- 

 sibly even less. On the west side of the Wabash river the conditions of 

 distribution are similar, though the strip of marl-loess is narrower, and 

 the maximum thickness of the common type occurs much nearer the 

 borders of the valley. The same thinning of the deposit away from the 

 river is noted, the common loess being quite frequently absent, at least 

 in recognizable amounts, at a distance of 15 miles from the Wabash. 



The common loess is not confined to any one horizon, but occurs at 

 all elevations from the level of the river bottoms to the crests of the 

 highest hills. Above a certain altitude, which detailed observation has 

 shown to be approximately 500 feet above tide (120 feet above the river), 

 it constitutes the only silt noted. Below this level, especially near the 

 river, the common loess, though generall}^ occurring, is not, as has 

 been seen, necessarily present, the marl-loess which normally underlies 

 it forming the bulk of the silts. Going eastward from the river, there is 

 a persistent, though gradual, decrease in the thickness of the marl-loess, 

 the common type becoming at the same time of greater relative, if not 

 real, importance. 



3IARL-L0ESS 



Distribution and range. — The marl-loess occurs on both sides of the 

 Wabash river and upon the surfaces of the rock " islands " which project 



