tendency is accentuated when the pirate is favored by the dip of the 
rocks, but frequently occurs in spite of the dip in cases where the 
dip is gentle. It is probably true that the only essential of such capture is 
that two streams lie one higher than tie other in a region of soluble rocks 
sufficiently close to each other to permit the final entrance of some of the 
waiter of the one to the other. Hxamples of such piracy are by no means 
wanting in the Bloomington region. 
Fig. 12. A distant view of the Leonards Mill locality (igs. 8 and 9), showing 
the form of the valley. The water from the Shirley Spring (Fig. 7) crosses the 
foreground. 
In order to make these specific cases fully intelligible it is necessary to 
refer to some length to the physiographic history and conditions of the 
region. The well preserved plain west of Bloomington appears to be a very 
early Pleistocene peneplain. This plain extends at about the same altitude 
throughout the extent of the map, except that it is visibly beveled toward 
the major drainage lines, as will appear later. The peneplain is much dis- 
sected in the nertheastern, southeastern, and western parts of the quad- 
rangle. There are mauy monadnocks to be found along the old divides or 
near the headwaters of some of the minor streams, rising from a little 
over a hundred feet to two hundred feet or more above this old plain and 
