189 



Volume of the Ancient Wabash River. 



Wm. A. McBeth. 



The Wabash valley at Terre Haute has a width of five to six miles. One- 

 third this width has a depth of approximately one hundred feet, embracing 

 a flood plain tract through which the river meanders in a channel averaging 

 one thousand feet wide and twenty feet deep. The remaining half is a terrace 

 about half the depth of the deeper part. The whole valley bottom shows the 

 effects of stream deposition, the pre-glacial trench of two hundred to two 

 hundred and fifty feet in depth being half-full of sand and gravel. A point 



Miles, i v * n £ 6-F&& 



J-, - 



jerttroliaed profile across Wabash Valley <& Terre ^aute. 



of interest in connection with the stream and valley is the question of volume 

 of water by which various phases of the work was done. The size and weight 

 of pebbles in the gravel indicate a volume and velocity much greater than 

 that of the present stream either in average volume or flood. Some suggestion 

 as to the width and depth of the stream at its stage of greatest flow is furn- 

 ished by features of the terrace surface consisting of sandbars and delta 

 deposits. This terrace surface is marked with numerous shallow current 

 lines or channels. The bars form ridges of greater length than width, often 

 many times longer. They trend northeast, southwest, the direction of the 

 valley and have the characteristic stratified structure of such features, the 

 layers of finer or coarser sand dipping steeply down stream. Extensive 

 areas of the terrace surface lie at an elevation of four hundred and ninety 

 feet a.t.l. Some places are five feet lower while some of the ridge tops rise 

 to the five hundred and thirty foot level. Low water in the present stream 

 is four hundred and forty-five feet. Points in sections 3, 23 and 24 and a 

 bluff side delta of a brook crossed by Fruitridge avenue at the south edge 

 of Section 24, Town 12 N. Range 9 W., rise to nearly the five hundred thirty 

 foot level. Sandbars and deltas are built under water and the surface of the 

 stream in which these deposits were made must have been a few inches 

 and possibly several feet above the ridge and delta tops when they were 



