THE OVERTURNS IN THE DENVER BASIN 



(') 



By Junius Henderson 



Geological field work in the foothill region of the Denver Basin 

 has possibly been hampered to some extent by the assumption that 

 the overturn of certain formations — and the locally increased dip of 

 the higher strata in other cases — were caused by the tangential, or 

 nearly horizontal, pressure which is commonly supposed to have pro- 

 duced the mountain range. It is very possible that the direct effect 

 of gravitation has not received sufficient consideration. Without in 

 the slightest degree discrediting the lateral-compression theory of 

 mountain uplift, of which there is other evidence along the foothills. 



Fig. 1 (after figure in Monograph XXVII, U. S. Geol. Survey, p. il).—A shows effect of 

 vertical upward pressure, with dip of strata nearest the point of uplift greater than at a 

 more distant point. B shows effect of tangential pressure. 



it is worthy of notice that the overturning of strata flanking the foot- 

 hills, may, at least in many places, and in every instance with which 

 the writer is familiar, be, with good reason, ascribed to a very dif- 

 ferent cause. 



In Monograph XXVII, United States Geological Survey, Geology 

 of the Denver Basln^ the fact is pointed out that the strata at some 

 distance from the Archaean are generally tilted to a much higher 

 angle than those lying nearer the granitic axis of the range, and this 



(1) Reprinted by courtesy of the Journal of Geology, Vol. XI, No. 6, September-October, 1903. 



