-6- 



00.40 00.40 Enter Ottawa. Descend hill on curving road to level of 

 Pleistocene (Wisconsinan) terraces in the Illinois River 

 Valley. Terraces flooring the valley were cut by the Out- 

 let River of Lake Chicago. 



01.50 01.10 Junction of Route 23 with Illinois Route 71 and U.S. Route 6 

 (Norris Street). Continue straight ahead. 



01.70 00.20 Turn right on Michigan Street (one-way west). 



01.75 00.05 DANGEROUS INTERSECTION. Turn left on La Salle Street (one- 

 way south) . Continue south through business district (5 stop 

 lights) . 



02.35 00.60 La Salle Street turns left 45° onto Illinois River Bridge. 



02.70 00.35 DANGEROUS INTERSECTION. Turn right (west) at junction of 



Illinois Routes 23 and 71 at south end of bridge. Route 23 

 continues southward. We will continue on Route 71 (westward). 

 Follow Hitt Street, passing Allen Park on the right. Just 

 west of Ottawa, the lower three-fourths of the Illinois Valley 

 walls are composed of Pennsylvanian sediments while upper parts 

 consist of glacial drift. 



03.00 00.30 Chicago, Burlington & Quincy railroad tracks. Sandstone of 

 the Ordovician St. Peter Formation is exposed on the north 

 bank of the river. 



03.30 00.30 Large water-filled silica sand pit on left. The St. Peter is 

 widely known as a glass sand but is also used for foundry 

 sand, abrasives, silica brick, ceramic glazes, and ferro- 

 silicon. It is also used for fracture treatment of oil-bearing 

 formations to increase flow. Illinois ranks No. 1 in the 

 United States in glass sand production, and virtually all 

 is provided by the St. Peter of La Salle and Ogle Counties. 



03.90 00.60 Another water-filled pit on left. 



04.70 00.80 Quarry refuse on right bank of river. 



05.50 00.80 Cross Covel Creek. Sandstone of the St. Peter with dolomite 

 of the Platteville Group on top of it can be seen on both 

 sides of the road. Westward, beyond Covel Creek, the bluffs 

 are almost entirely bedrock. Approximately 1 mile west of here, 

 the top of the St. Peter appears at the base of the bluff. 

 Westward from there, the sandstone climbs the cliffs and 

 reaches the top in Starved Rock State Park. 



06.10 00.60 We are crossing the broad, flat Ottawa Terrace, which lies 

 between the inner channel of the Illinois River and the 

 uplands seen on the south. The terrace here is a bedrock 

 bench cut on the top of the St. Peter, which is covered 

 by only a few feet of soil, sand, and gravel. The Ottawa 

 Terrace records downcutting of some 50 feet by overflow of 

 glacial Lake Chicago. 



