206 Proceedings of Indiana Academy of Science 
continuous and alternate from side to side of the valley. These relief 
forms are in great contrast to the local sinkhole plains developed some 
50 to 100 feet above the valley floor of Indian Creek. 
The ridges of the area are composed chiefly of massive sandstones, 
though their lower and more gentle slopes are composed of the upper 
part of the Mitchell limestone. The sinkhole plains are developed ap- 
proximately 100 feet below the top of the Mitchell limestone, or near 
the top of the St. Louis geologic unit. The local sinkhole areas as 
shown in sections 8 and 17 are somewhat lower than those in sections 
4 and 9. This is in harmony with the dip of the strata to the southwest. 
Features accompanying subterranean drainage are very much in 
evidence. Possum Valley, a small portion of which is shown on the 
topographic sketch, is a streamless valley which lies east of Indian 
Creek valley. This valley offers some interesting physiographic phenom- 
ena. As a valley basin it is some 3 or 4 miles in length. It is rimmed 
by sandstone ridges with the exception of the opening on the south. 
Its floor is occupied by numerous sinkholes and swallow-holes. Small 
streams descend from the sandstone ridges and hills and enter the 
swallow-holes in the bottom of the valley. Some of the ravines or 
small streams are headed by springs which commonly issue from the 
foot of steep sandstone bluffs near the tops of the ridges. Two such 
springs are shown on the topographic sketch. South of the area covered 
by the topographic sketch the valley is open and is occupied by a 
normal surface stream, Hackley Creek, which enters Indian Creek a mile 
or so below. Little or none of the waters which drain into the swallow- 
holes enter Hackley Creek. These waters apparently enter Indian Creek 
Fig. 3. View showing the pool in Indian Creek channel in which the waters sink. 
During low water condition all the water enters the subterranean channels here and 
passes southward beneath “‘Boogers Point’’, re-entering the surface channel of Indian 
Creek after passing through a subterranean channel or channels one-fourth mile in 
length. The fall of the subterranean route is approximately twenty feet. The route 
taken by the surface stream during higher water stages is 3.1 miles in length. (See 
Bigss4.) 
