180 UNIVERSITY OF COLORADO STUDIES 
intelligent prospecting along the 
plains bordering the foothills of 
eastern Colorado, but the prospect- 
ing thus far has resulted in a vast 
amount of dead work upon which 
the comparatively few producing 
wells must pay interest in order to 
make the industry on the whole a 
profitable one. The accumulation 
of oil in the rocks is known to be 
controlled largely by folds. The 
great thickness of this formation, its 
homogeneity and the lack of closely 
connected outcrops over large areas 
render the accurate determination 
of such structural features very 
difficult. For this and other reasons 
the prospecting has thus far been 
carried on chiefly by haphazard 
boring, the location of many borings 
having been based upon the use of 
the ‘‘bobber,”’ the finding of horse- 
shoes and rabbit tracks and other 
superstitious methods. In conse- 
quence many holes have been put 
down where more thorough and sys- 
tematic prospecting would have 
shown their probable folly and more 
likely ground has been wholly over- 
looked. Where the oil is reached at 
a depth of hundreds of feet, as here, 
the expense of dry holes is an item to 
be seriously considered. Hence the 
growing demand for a better under- 
standing of the Pierre formation. 
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Fic. 1.—Map showing relation of Hygiene sandstone to older formations of foothills, prepared by Mr. H. F. Watts from the writer’s data. 
