LANDSLIDES OF TH" RICO MOUNTAINS, COLORADO 583 



Remarks were also made by J. B. Woodworth, A. C. Spencer, and the 

 President. 



The third paper was 



TOPOGRAPHIC FEA TUBES OF OHIO 

 BY W. G. TIGHT 



The subject was discussed by M. R. Campbell, I. C. White, and the 

 author. 



The next paper was. by the same author, as follows : 



DRAINAGE MODIFICATIONS IN SOUTHEASTERN OHIO 

 BY W. G. TIGHT 



Remarks upon this paper were made by M. R. Campbell, I. C. White, 

 and the author. 



The following paper was then read : 



LANDSLIDES OF THE RICO MOUNTAINS, COLORADO 

 BY WHITMAN CROSS 



[Abstract with discussion'} 



The Rico mountains, in southwestern Colorado, are due to the erosion of a local 

 domatic uplift. The sedimentary formations affected embrace the Algonkian, De- 

 vonian, Carboniferous, Permo-Carboniferous, Juratrias, and Cretaceous. Many 

 intrusive dikes, sheets, and small laccoliths of diorite — or monzonite— porphyry 

 occur in this complex. A large monzonite stock penetrates all rocks above men- 

 tioned. Intense and complicated faulting has taken place in the heart of the uplift, 

 and there has been a great amount of mineralization, forming argentiferous ore 

 bodies of many types. 



Landslides, occurring in a recent geological epoch, are very prominent features 

 of the local geology. These landslide areas will be described, the relation of the 

 phenomena to other elements of the geological history will be discussed, and 

 hypotheses of their origin set forth in the paper when printed. 



In the discussion of the subject of Mr Cross' paper, Mr J. B. Wood- 

 worth said in substance : 



Landslips occur near the head of Warm Springs creek, in the Gravelly range in 

 Montana. Here the movement has taken place on westward dipping water- 

 bearing Cretaceous strata. The slides simulate small moraines, enclosing lakelets, 

 and might be mistaken for glacial deposits, which also occur in the vicinity. 



Mr George Otis Smith spoke as follows : 



In the Mount Stuart quadrangle in Washington the occurrence of landslides is 

 the rule rather than the exception. Professor Russell first called attention to these 



LXXXII— Bull. Geol. Soc. Am., Vol. 11, 1899 



