PAPERS GX GEOGRAPHY AND GEOLOGY 327 



THE ORIGIN OF THE CAHOKIA MOUNDS 

 (ABSTRACT) 



Morris M. Leighton, Illinois Geological Survey, 



Urban a 



During the recent explorations which have been car- 

 ried on by Doctor W. K. Moorehead of Andover, Massa- 

 chusetts, under the auspices of the University of Illinois, 

 four widely scattered mounds of the Cahokia group, 

 northeast of St. Louis, ranging in height from 10 to 35 

 feet, have been trenched and opportunity afforded for 

 the study of their constitution, structure, and in one case, 

 their relations to the underlying materials of the allu- 

 vial filling of the Mississippi Valley. The Illinois Geo- 

 logical Survey was invited to make a geological examina- 

 tion, resulting in the accumulation of evidence decisively 

 favoring the artificial mode of origin of at least those 

 mounds which have been opened and examined. This 

 conclusion is re-enforced by the artificial form of the 

 mounds, their orientation, their grouping, and their 

 geologic setting. Monks Mound, the dominating unit of 

 them all, has not as yet been trenched or tunneled, and 

 hence a positive conclusion can not be drawn as to its 

 origin : but the materials revealed by auger borings made 

 by the writer on the summit and slopes of the mound and 

 its artificiality of form are suggestive that at least a large 

 part of it is due to the work of man. 



A full report of the geologic aspects of the Cahokia 

 Mounds is now in press and will appear as Part II of a 

 bulletin of the University of Illinois which treats of the 

 explorations made up to and including the fall of 1922. 



