264 



deep. The slopes of valley sides are generally steep and the ravines of 

 the ultimate tributaries are exceedingly narrow and sharp. The depth of 

 the glacial drift is generally from 40 to GO feet, and the streams only here 

 and there touch bed rock. 



Many beds of recent conglomerate appear along west Little Sugar 

 creek. The principal valleys are -preglacial, with a base level determined 

 by the level of the preglacial Wabash, which was 60 or 70 feet lower than 

 the present river. These valleys were filled with drift which the post- 

 glacial streams have scarcely half removed. The drainage has developed 

 by headward erosion into an intricate, dendritic system of insequent 

 branches which penetrate to nearly every acre of the area. Judging from 

 the position of large trees there is reason to believe that the Hues of drain- 

 age were well defined before vegetation sprang up. 



Stratigraphy. — The underlying bed rocks of the area are the shales 

 of the coal measures with several workable seams of coal, the uppermost 

 of which outcrops along the foot of the Wabash bluffs. The shales above 

 the coal form about one-half the height of the bluffs. The upper half 

 consists of glacial drift. Intercalated with the shales are several thin 

 strata of limestone, two of Which exercise a notable influence upon the 

 topography. Below the 500-foot level a tough, flinty limestone four or five 

 feet thick has resisted river erosion to such an extent as to form a terrace 

 between the Wabash flood plain and bluff, in some places 500 feet wide 

 and 20 feet above the plain. We call it the flinty limestone. A similar 

 but less silicious limestone lies about thirty feet higher. In section 31 

 the waters of the Sugar creek system have cut a gap in these strata and 

 reach the Wabash at grade. 



The glacial drift belongs to the Illinoian drift sheet of Leverett and 

 lies just outside the border of the Shelbyville moraine. The mass of it 

 consists of a tough boulder clay, weathering on exposed faces into roughly 

 hexagonal columns and containing numerous striated and faceted boulders 

 of moderate size. Large boulders are rare. In some places the till is one- 

 half fine gravel. There are occasional thin partings of sand. In a rail- 

 road cut about one mile to the north of the area surveyed buried logs of 

 wood up to nine inches in diameter are numerous along a level horizon, 

 but no difference can be discovered between the overlying and the under- 

 lying till. In the south bluff of Sugar creek beds of laminated silt are 

 intercalated in the till and point to the occurrence of an interglacial in- 

 terval of notable extent. The upper four or five feet of drift often con- 



