MARL-LOESS 157 



above its flood plain. On the west, though occurring at all altitudes up 

 to 500 feet above tide, or 120 feet above the river, it is developed to a thick- 

 ness probably nowhere exceeding 30 to 40 feet, and except near the imme- 

 diate borders of the valley, is usually less than 10 feet. It extends back 

 several miles from the river, but, because of its slight development, its 

 precise limits could not well be determined. Good sections of a very 

 silicious form of the marl-loess are to be found in the bluffs at Mount 

 Carmel, while the more calcareous type forms numerous flats standing 

 some 30 or 40 feet above the Wabash plains from mount Carmel south- 

 ward to Rochester. 



East of the Wabash river the marl-loess reaches its greatest develop- 

 ment just south of New Harmony, where it forms bluffs rising to the 

 500-foot level. It does not appear probable, however, that the height of 

 the somewhat receding bluff is indicative of the actual thickness of the 

 marl-loess, for well records on the top give 10 to 25 feet as a common 

 depth to the rock or to the Illinoin till upon which the silts rest, though 

 occasional depths of " marl and blue mud," the latter possibly being a 

 variety of the marl-loess, are reported as high as 50 feet. The marl-loess 

 constitutes the surface formation along the uplands bordering the Wa- 

 bash flats at many points from New Harmony northeastward to Hazelton 

 and eastward up the White river to Petersburg, reaching frequently to 

 an altitude of 500 feet above tide, but never above. Beyond Petersburg 

 it has not been traced. 



The belt-like character of its distribution appears to be controlled by 

 a coincident belt of highlands, of which the inequalities and all but the 

 higher portions have been buried beneath the plateau-like plains of 

 marl-loess. 



The superficial continuity of the marl-loess is frequently interrupted 

 by areas of dune sand of a late Wisconsin stage, but as the sand is known 

 in many cases to rest upon the marl-loess, it is extremely probable that 

 the deposit of the latter is essentially continuous within the limit men- 

 tioned. It reaches thicknesses of 40 feet or more at Hazelton, and ap- 

 pears to be of a somewhat similar thickness along the bluffs 2 miles 

 northwest of Patoka. The marl-loess also reaches similar altitudes and 

 perhaps equal or greater thicknesses on the numerous " islands " of the 

 Wabash flood plains, among which may be mentioned the Claypole, 

 Gorden, and Mumford hills. In all localities noted the marl-loess is 

 thickest where nearest the Wabash, and gradually decreases until it thins 

 out and disappears, except perhaps for an occasional thin bed, at a dis- 

 tance of 5 to 8 miles from the borders of the river flats. Its eastern limit 

 in the Claypole, Gorden, and Mumford hills has been determined by 

 subsequent meanderings of the Wabash river, which have undoubtedly 



