204 



Borings at Terre Haute pass through 130-150 feet of gravel and at 

 Lyford 160 feet. The structure as exposed in excavations is coarse sand 

 and fine gravel, poorly stratified and exhibiting a great variety of cross- 

 bedding in which the dip is nearly everywhere down stream. At Terre 

 Haute the principal bedding is nearly regular, the average thiclvness of 

 each bed seldom being more than one foot. (Fig. 7.) At Lyford the 

 material is distinctly coarser and gives evidence of having been laid down 

 by turbulent and rapidly changing streams, as shown in the section. (Fig. 

 3.) Imbedded in the gravel are crystalline boulders up to 2 or 3 feet in 

 diameter and many rounded masses of boulder clay up to 10 feet in 

 diameter. Here also are found numerous fragments of hard limestone, 

 Mansfield sandstone, bituminous shale and coal which are absent or rare 

 in the vicinity of Terre Haute. 



Surface drainage on the terrace is wanting or very imperfect. Small 

 streams which come down through the bluff are unable to make their way 

 across the terrace and are lost in the shallow depressions between the 

 ridges. Stronger streams, like Otter Creek and Spring Creek, have cut 

 deep valleys through the terrace and maintain a perennial flow. 



The Terre Haute terrace is only one among many similar features, but 

 in many respects belongs to a class by itself. It alone is moraine-headed, 

 holding the relation of a valley train to the Shelbyville moraine. It 

 possesses some, but not all, of tlie characteristics of a typical valley train. 

 It thins out from 160 feet in depth at Lyford to nothing at its lower end, 

 which gives it a longitudinal slope from 550 feet A. T. to about 450 feet, or 

 a fall of 100 feet in 27 miles. It is composed of somewhat coarser material 

 at its head than at Terre Haute, and near the moraine its surface is pitted 

 with a few small pond basins where detached ice blocks may have melted 

 away. Its longitudinal sand bars are evidence that its surface topography 

 is due to a broad stream wliich once entirely covered it, standing above 520 

 feet A. T. This greater Wabash was fed not only by the main Wabash 

 stream, but also by a tributary half as large from the present Raccoon 

 Valley to be described in ;iiio(li('r ]i;iihm'. These two str(>anis came together 

 at the south end of Athertoii Island and built up between them a bar 5 

 miles long and a mile wide with characteristic mounds and undrained 

 saucer shaped hollows. The old Raccoon channel between this bar and the 

 east bluft' is a dei)ression a mile wide and 30 f<M>t deep, now occiiiii(>(l by a 

 nameless tributary of Otter Creek. 



