168 FULLER AND CLAPP MARL-LOESS OF LOAYER WABASH VALLEY 



Four possible assumptions as to the cause of the hugging of the west 

 bank by the current suggest themselves : (1) It was entirely accidental ; 



(2) the current followed the laws of deflection due to the earth's rotation ; 



(3) it was governed by a coincident preglacial channel ; and (4) it was 

 deflected to the west by meeting the overflow of the Ohio from the east. 

 An intimate knowledge of the conditions along other portions of the 

 Wabash, as well as the Illinois, Missouri, and Mississippi rivers, would 

 very likely furnish valuable evidence bearing on the probable condi- 

 tions, but in the absence of such knowledge, nothing definite can be 

 stated beyond the fact that, if the area under discussion is considered by 

 itself, it would appear most probable that the position of the current was 

 due to a combination of the last two or perhaps of all but the first of the 

 postulated conditions. 



The excessive accumulation of the marl-loess near New Harmony ap- 

 pears to have been due to the presence there of a high rock and morainal 

 ridge parallel to the Wabash valley and reaching occasionally above the 

 500-foot level. This ridge not only formed a nucleus for the deposition, 

 but was the cause of slack water conditions especially favorable to the 

 accumulation of the silts. The absence of the marl-loess as a recogniza- 

 ble type beyond a moderate distance (5 to 8 miles) from the Wabash 

 valley is thought possibly to be due to the failure of the silt-laden cur- 

 rents to pass through into the almost inclosed body of water lying to the 

 east behind and protected by the rocky barrier mentioned. 



CA USE OF THE PONDING 



There is no evidence in the Wabash region of the cause of the ponding 

 of the waters to the 500-foot level. Among those who have studied the 

 conditions along the Mississippi valley, some have suggested local bar- 

 riers due to warping, but no reliable evidence appears to have been pre- 

 sented. A general depression of the northern portion of the United 

 States relative to the land to the south across which the waters eventuall}^ 

 had to pass, and due to or at least accompanying the lowan ice-sheet, is 

 perhaps not improbable, although it is very difficult to prove. The loess 

 terraces, plains, etcetera, described* by Bain, Call, Calvin, Chamberlin 

 and Salisbury, Ha3^den, Hershey, McGee, Todd, and White suggest that 

 similar conditions existed over considerable portions of the Mississippi 

 basin. 



DERIVATION OF THE MATERIALS 



The absence of probable sources, either to the east or to the west, 

 seems to make it clear that, as has been already pointed out, the mate- 



* See papers 1, 4, 6, 11, 15, 21, 28, 29, 30, 31, and 32 of bibliography at end of this paper. 



