104 GEOLOGY OF ILLINOIS. 



Sand and Clay. — Clays suitable for making brick may be fouud almost 

 anywhere in the subsoil of the uplands, and sand for mortar or cement 

 occurs abundantly in the valleys of the streams. 



Soil and Timber. — In the southern part of the county the soil is rather 

 thin, with a subsoil of light drab-colored clay, but in the northern por- 

 tion it is darker colored and more productive, and has a subsoil of yellow 

 clay. Much of the prairie and a portion of the timbered land is rather 

 flat and requires thorough draining to make it productive. The bottom 

 lands on the Bmbarras are from a half mile to a mile or more in breadth, 

 and were originally covered with a heavy growth of timber, but portions 

 of it have been cleared and brought under cultivation, and are very 

 productive, though subject to occasional overflow. The varieties of 

 timber in this county appeared to be about the same as in Clark, and 

 need not be enumerated again here. A supply of water may usually be 

 obtained in the gravelly drift clays above the hard pan, but at some 

 localities it can only be had by boring or digging through the hard pan 

 to the quick sands below. 



Coles County embraces au area of over five hundred square miles, 

 and is bounded on the north by Douglas county, on the east by Edgar 

 and Clark, on the south by Clark aud Cumberland, and on the west by 

 Moultrie and Shelby. The principal water courses in the county are 

 the Embarras river, which traverses its eastern portion from north to 

 south, and the Okaw or Kaskaskia, which runs diagonally across the 

 north-western corner of the county. The greater portion of its surface 

 is prairie, though there are belts of excellent timber skirting all the 

 water courses, and the southeastern part of the county along the 

 Embarras and its tributaries is heavily timbered. 



This county lays in that portion of the State where the drift deposits 

 attain nearly to their maximum thickness, and bowlders of considerable 

 size are quite commonly to be seen on the surface of the prairies but 

 partially imbedded in the soil. The total thickness of the drift in this 

 county ranges from fifty to one hundred and fifty feet or more, the upper 

 part consisting of a variable thickness of brown or buff gravelly clays, 

 and the lower of blue clays or hard pan, the latter sometimes underlaid 

 by gravel and quicksand. 



In the boring for oil at Charleston, fifty-five feet of drift was reported 

 as follows : 



Ft. 



Soil and yellow clay 18 



Sand and gravel 8 



Blue clay (hard-pan) 16 



Bowlder clay , 13 



At Mattoon, wells have been sunk from seventy-five to one hundred 

 and fifty feet without reaching bed rock, and all the way through drift 



