10 ILUNOIS BIOLOGICAL MONOGRAPHS [108 



PHYSICAL FEATURES OF THE BIG VERMILION BASIN 



The Big Vermilion River drains about 1,500 square miles in Champaign, 

 Ford, and Vermilion counties in Illinois and a small portion of Warren and • 

 Fountain counties, Indiana. The North Fork also drains from a small 

 territory in the southeastern part of Iroquois County, Illinois. The main 

 stream, known as Middle Fork, rises in the southern part of Ford County 

 near the town of Melvin, in the Bloomington morainic system, at a height 

 of 800 feet above sea level. Its course is southeastward, between the hills 

 of the moraine known as the Roberts and Melvin ridges, passing through 

 the latter and uniting with a tributary known as the West Branch of the 

 Middle Fork, which also rises at an elevation of 800 feet in the Roberts 

 ridge. At Potomac, the stream turns southward, cuts through the outer 

 ridge of the Bloomington moraine and crosses the plain of the Champlain 

 till sheet, uniting with the Salt Fork about six miles west of Danville. 



The largest western tributary, known as the Salt Fork, rises in the till 

 plain in the north-central part of Champaign County, near Thomasboro, 

 at an elevation of about 740 feet above the sea. It drains the till plain 

 lying between the Bloomington moraine on the north and the Champaign 

 moraine on the south. It flows in a south and east direction for about 

 55 miles^ and unites with the Middle Fork as described above. A large 

 tributary of Salt Fork, known as Spoon River* rises in the northeastern 

 part of Champaign County, in two branches, not far from the outer ridge 

 of the Bloomington moraine. Its general course is southward for a dis- 

 tance of about ten miles, where it unites with the Salt Fork near St. Joseph. 



Another large tributary is known as the North Fork, which rises in the 

 southeastern comer of Iroquois County in the inner ridge of the Blooming- 

 ton moraine. It flows southward, cutting through the middle and outer 

 ridges of the moraine, crosses a part of the Champaign till plain and unites 

 with the Big Vermilion at Danville. This tributary has a length of about 

 40 miles. From Danville the larger stream flows southeastward for about 

 20 mUes, crossing a part of Vermilion County, Indiana, and empties into 

 the Wabash River 10 miles from the Illinois State line. 



The basin of the Big Vermilion River lies in or is surrounded by glacial 

 moraines of the Early Wisconsin glaciation, the Bloomington moraine on 



» Length of rivers designates total length including all meanders. 

 ' Not to be confounded with Spoon River entering the Illinois River near Havana, Mason 

 County. 



