January 19, 1900.] 



SCIENCE. 



101 



the tributaries of this preglacial river were 

 also described. 



The paper gave a very graphic conception 

 of the rearrangements which were brought 

 about by the continental ice sheet, chang- 

 ing the outlet of the river system from the 

 Great Lakes to the Mississippi. In discus- 

 sion M. E. Campbell brought up the Teazes 

 valley and the changes in the Big Kanawha, 

 and the presence of silt in the former. W. 

 G. Tight then described the area covered 

 by silt and referred the readjustment of the 

 drainage to the obstruction which it pre- 

 sented. The silting was explained by some 

 barrier far to the westward. I. C. White 

 referred to his early description of the val- 

 ley, and urged the danger of mistaking, for 

 cols, narrows in the Ohio and other rivers 

 produced by the crossing of some hard 

 stratum. The author replied that he had 

 sought to guard against this. 



The landslides of the Rico Mountains, Colorado. 



By Whitman Cross, Washington, D. C. 



The Rico Mountains, in southwestern 

 Colorado, are due to the erosion of a local 

 domatic uplift. The sedimentary forma- 

 tions aifected embrace the Algonkian, 

 Devonian, Carboniferous, Permo-Carbonif- 

 erous, Juratrias and Cretaceous. Many 

 intrusive dikes, sheet's and small laccoliths 

 of diorite — or monzonite — porphyry occur 

 in this complex. A large monzonite stock 

 penetrates all rocks above mentioned. In- 

 tense 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 geo- 

 logical epoch, are very prominent features 

 of the local geology. These landslide areas 

 were described, the relation of the phe- 

 nomena to other elements of the geological 

 history were discussed, and hypotheses of 

 their origin set forth. 



The landslides are limited to the central 

 portion of the domatic uplift. No apparent 

 connection can be traced between the struc- 

 ture and the slides, nor are they present 

 in the region of greatest faulting. The 

 speaker finally concluded that they were 

 connected with deep, interior vulcanism, 

 transmitted through the intruded stock of 

 monzonite. 



J. B. Woodworth mentioned similar cases 

 in southwestern Montana, where water- 

 bearing beds caused the slipping. W. M. 

 Davis mentioned Alpine cases where glac- 

 ial erosion had removed the support. Dr. 

 Cross said there was no glaciation at Rico. 

 W. H. Niles also referred to Alpine cases. 

 Geo. Otis Smith mentioned similar cases in 

 the Stewart mountains, Oregon, where, of 

 all the rocks present, the granite is alone 

 unafl'ected. 



A recent fault scarp in the Lepini Mountains, 



Italy. By W. M. Davis, Cambridge, 



Mass. 



The Lepini mountain group is a sub- 

 maturely dissected block of cretaceous 

 strata, 40 miles S. E. of Eome. Recent 

 movement on the line of a tertiary fault 

 has produced a well-defined scarp in places 

 100-200 feet in height and traceable five 

 miles or more along the northeastern base. 



The paper was finely illustrated by the 

 lantern and the truncations of fan-like pro- 

 jections of rock called rock-fans were well 

 shown. There was no discussion. The 

 reading of the paper closed the first day's 

 proceedings. 



On Wednesday evening the President, 

 Professor B. K. Emerson, delivered his 

 presidential address upon ' The Tetra- 

 hedral Earth and the Zone of the Inter- 

 continental Seas,' before a large gathering 

 of the Society and their friends. It will 

 appear in another number of Science. 



The Society convened in business session 

 Thursday morning at 9.30 o'clock. The 



