November 29, 1895.] 



SCIENCE. 



719 



the Fountain formation. No fossils are 

 known in them. 



The strata of the Juratrias and Cretace- 

 ous have been found in remnants upon the 

 granite plateau, indicating a former exten- 

 sion of these beds connecting witli South 

 Park; 



Eocene. ' The small lake deposit about 

 Florissant is noted the world over for its 

 fossil insects, while fishes, birds and many- 

 plants are also found in these thin beds, 

 which are chiefly made up of volcanic 

 ashes. 



The volcanic rocks of the district are 

 numerous and interesting. Those of the 

 western portion belong to a great volcanic 

 center south of South Park. At Cripple 

 Creek is a local volcanic vent, the peculiar 

 product of which is the rare rock phonolite. 



Many points in the geological historj' of 

 the Colorado Eauge have been brought out 

 by the recent survey, such as the evidence 

 of varying relations between land and sea at 

 different periods, shown by unconformities 

 and by remnants of strata on the granite 

 plateau. The shear zones shown by the 

 gneisses, and the observed folds and faults 

 of the foothills, bear directly upon the struc- 

 tural history of this portion of the Rocky 

 Mountains. 



Economic Geology. — The gold-bearing dis- 

 trict of Cripple Creek is directly connected 

 with the volcanic center. The gold ores 

 are free milling near the surface, but pass 

 into telluride smelting ores in depth. They 

 occur in veins, chiefly in the volcanic rocks, 

 but occasionally in the granite near them. 

 The extreme alteration of the rocks of the 

 eruptive center, and the unusual character 

 of the gold veins, have made a detailed 

 study of the mining district necessary. A 

 special topographic and geologic map on the 

 scale 3jg J^rru) or nearly 2h inches to the mile, 

 has been made, and the ore deposits have 

 been thoroughly examined by Prof. R. A. 

 F. Penrose, Jr. 



FOLIO 9, ANTHEACITE-CEESTED BUTTE, COLO- 

 RADO, 1894. 



This double folio consists of 3 pages of 

 text descriptive of the Elk Mountains, by 

 S. F. Emmons: 2 pages descriptive of the 

 igneous formations of the two districts, by 

 Whitman Cross ; 4 pages descriptive of the 

 sedimentary formations, by G. H. Eldridge; 

 of each of the two districts a topographic 

 map (scale 1:62,500), a map of areal 

 geology, another of economic geology, and 

 a third of structure sections ; and finally, a 

 sheet showing a generalized columnar sec- 

 tion for the two districts. 



Geography. — The combined area repre- 

 sented on the two sheets covers one-eighth 

 of a degree, lying between the parallels 38° 

 45' and 39° and the meridians 106° 45' 

 and 107° 15', and is about 21\ miles long 

 from east to west and 171 from north to 

 south. It includes the southern third of 

 the Elk Mountain group, which lies be- 

 tween the Sawatch Range on the east and 

 the plateau of the Colorado basin on the 

 west. It is a highly picturesque and moun- 

 tainous region, and, like the San Juan 

 Mountains to the south, has a more abun- 

 dant precipitation and is more alpine in its 

 character than other parts of the Rocky 

 Mountains. 



The northern half of the eastern or 

 Crested Butte tract is occupied by the 

 southern portion of the Elk Mountains 

 proper, whose culminating points have an 

 elevation of over 13,000 feet ; the south- 

 eastern portion of that tract includes the 

 distinct and less elevated Cement Moun- 

 tain uplift. The rest of this area and the 

 whole of the Anthracite tract is occupied 

 by more or less isolated mountain peaks — 

 Crested Butte, Gothic Mountain, Mount 

 Wheatstone, etc., and by one prominent 

 north-and- south ridge, the Ruby Range, 

 whose higher summits rise between 12,000 

 and 13,000 feet above sea level. 



The drainage of all this area finds its 



