164 PROCEEDINGS OP THE ALBANY MEETING 



SILVER CITY QUARTZITES, A KANSAS METAMORPHIG AREA 

 BY W. H. TWENHOFEL 



(Abstract) 



Silver City, Kansas, an abandoned mining camp, is underlain by altered 

 sedimentary rocks, which consist chiefly of quartzites ; but one member of the 

 sequence is a breccia, the cement of which is composed of quartz, chlorite, and 

 hornblende. The altered area is about 200 yards wide and less than a mile 

 long. The surrounding strata are unmodified. 



The evidence leads to the conclusion that the change is due to hjdrothermal 

 action. 



The occurrence is of interest because of the rarity of metamorphic rocks 

 within that section of the country. 



Presented in abstract extemporaneously. 



OROGRAPHIC ORIGIN OF ANCIENT LAKE BONNEVILLE 

 BY CHARLES E. KEYES 



(Abstract) 



A recent inquiry into the derivation of certain features of the Great Basin, 

 Great Salt Lake, and especially its precursor, the vaster Lake Bonneville, pre- 

 sented some seeming anomalies which, from a perusal of the literature alone, 

 could not be readily adjusted to the modern genetic scheme of physiographic 

 development. This circumstance eventually led to several special visits to the 

 Utah field and a critical examination on the ground of the published data 

 relating to the geologic history of the old desert, lake. In the prevailing 

 hypothesis concerning the origin of Lake Bonneville so many incongruities 

 were found as to compel its abandonment. Instead of a genesis due to con- 

 ditions of moister climate induced by a glacial epoch, the facts gathered seemed 

 to point not only to a pre-glacial date of the lake's birth, but to a diastrophic, 

 rather than a climatic, cause for the lake's existence. 



The conclusions reached are that the great body of water of which Great 

 Salt Lake is a last vestige is not, after all, an anomaly among desert features, 

 but that it merely represents a special phase of a through flowing stream that 

 was not quite large enough to master the orogenic barrier which chanced to 

 arise athwart its path, while its nearest neighbor and parallel stream, the 

 Green River, reinforced by the Grand and other large eastern tributaries, was 

 sufficiently powerful to hold its own against all vicissitudes and to carve 

 through the rapidly bulging Colorado dome a Titan among chasms. Blocked 

 by such a formidable rampart, the old Virgen River spread out far and wide 

 over the adjoining intermont plains. Finally, the principal headwaters being 

 diverted, the waters of the great lake evaporated until equilibrium was again 

 established with the tributaries now greatly reduced. 



Presented by title in the absence of the author. 



