Silurian Reef at Thornton, Illinois
Outcrops

Reef core at Thornton Quarry with flank beds dipping (inclined) in opposite directions off the core. The tunnel leads to another quarry pit. Note the two people standing at the base of the quarry wall (in the circle).


View of the northwestern part of the Thornton Quarry; red boxes on quarry floor are about 2 m high. Closely-spaced, light-colored vertical lines are drillholes. Left to right inclination of flank beds is also visible.


Inclined flank beds of the reef overlying nearly horizontal pre-reef deposits. As at Racine, flank beds contain abundant crinoid debris. Note pick-up truck for scale.


A large, dark-colored boulder within flank beds. Boulders were emplaced by sliding down the flank of the reef. They contain abundant corals and stromatoporoids and were derived from the reef crest.



© 1997, Milwaukee Public Museum, Inc.