A NOTE ON A SINK HOLE 
E. J. CABLE 
Most sink holes occur in regions where the underlying rock is 
dominantly calcareous. They are variously shaped depressions 
in the surface into which the run-of¥ is carried away as sub- 
terranean drainage. 
Sink holes are due, (1) to an enlargement by solution of joints 
and fissures, or, (2) to the caving in of the tops of subterranean 
caverns. They vary in diameter from a few yards to several 
miles. Where sink holes are due to the solvent action of meteoric 
waters along joints or fissures they are more or less round, but 
wheredhey result from the caving in of the roofs of subterranean 
caverns, they are more irregular in outline. After their formation 
many sinks are given dendritic pattern by the erosive work of 
surface streams which flow into them. 
Often sink holes become clogged, due either to a filling up of 
the joints or fissures, or to a sudden rise of the ground water 
surface. In such instances lakelets are formed. 
Sink holes are common in many parts of Iowa. In the north- 
eastern part of the state where the glacial and residual rock 
mantle is thin and the underlying rock is highly calcareous, sink 
holes, in places, are the most conspicuous features of the land- 
scape. 
In some parts of the state farmers have attempted to drain 
small ponds and marshes on their land by boring holes through 
the more or less impervious rock mantle and thus connecting the 
surface drainage with the subterranean fissures and joints. In 
some instances where the sink holes become an asset for surface 
drainage, farmers direct their tile ditches into these sink holes. 
In the spring of 1918, a peculiar sink hole was observed in 
Pocahontas county. The county is deeply covered with drift 
except in local areas where the underlying St. Louis limestone 
is subject to the solvent action of meteoric waters. The sink 
hole in question is located seven and one-half miles to the south 
and east of the town of Rolfe. 
Instead of proving ready egress for surface waters the sink 
