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 60 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 lines 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- 
iying 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 fiye feet of drift often con- 
