BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 16, pp. 205-214 April u, 1905 



EFFECT OF CLIFF EROSION ON FORM OF CONTACT 



SURFACES 



BY N. M. FENNEMAN 



(Read before the Society December 80, 190 Ji) 

 CONTENTS 



Page 



The area studied 205 



Observations in the field 205 



Effect of preexisting topography 206 



Factors and conditions of the problem 206 



Illustrative cases of submergence conditions 208 



In general 208 



Case I. Shore recession more rapid than shifting by submergence 208 



Case II. Recession progressively retarded until its rate equals that of 



shifting 209 



Application of case II to the area studied 211 



Case III. Recession less rapid than shifting by submergence 211 



Generalization 212 



The Area studied 



The occasion of this study was an attempt to determine the relations 

 of the Wyoming Red beds to the underlying granite in the Front range 

 of the Rocky mountains in northern Colorado. The southern half of 

 the Boulder and the northern part of the Denver quadrangles represent 

 the area of investigation. 



Observations in the Field 



It was evident from the nature of the variations in thickness of the 

 sandstones that the sediments were laid down on a submerging land sur- 

 face of considerable relief. It was also apparent that the details of this 

 relief were totally unlike the forms produced by stream erosion. The 

 rocks immediately below the contact surface are as free from weathering 

 as those which lie hundreds of feet lower. It is therefore evident that 

 during the progress of the submergence of the granite land surface, shore 



XXVIII- Boll. Gbol. Soc. Am., Vol. 16, 1904 (205) 



