62 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
Park the writer is inclined to the belief that they are thin residual 
patches of a larger mass that once covered that entire area. South- 
east of Boulder Park are two patches of gravel that extend toward it, 
while farther to the southwest are gravel areas, mapped by Professor 
Jaggar, which lie on the general divide between Bear Butte and Park 
Creeks. Other patches mapped by him lie northwest of Deadwood 
and illustrate very well the characteristic habit of occurrence on the 
present stream divides. The arrangement of gravel areas, thus 
indicated, is suggestive of a former trunk stream, flowing east-north- 
east, with branches from the west and south. 
The northward extension of the main gravel body makes a distinct 
inclination eastward at the head of Crook valley and reaches well up 
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AY 
Fra. 1. Index map of Black Hills district, 
on the flanks of the anticline, which forms its eastern side. Farther 
to the northwest there are two patches of gravel on the sides of Crook 
valley near its junction with Whitewood Creek, while other significant 
patches occur on the shoulders of Whitewood valley three miles west 
of Crook Mountain. These smaller gravel deposits, together with 
the eastward extension of the main body, already noted, have an 
important bearing on the story of capture, which forms so interesting 
a chapter in the drainage history of the region. 
Sources. It will be seen from the map (Plate 1) that possible sources 
of all the types of pebbles found lie within the present drainage basins 
of Whitewood and Bear Butte Creeks. It is not necessary, therefore, 
to extend the limits of the ancient drainage area. The lines on the 
map that diverge from a numbered locality show the direction and 
range of sources from which its pebbles were derived. ‘The data at 
