4 SURVEY OF COLORADO AND NEW MEXICO. 



out their relations by studying the junction of the changed with the 

 unchanged rocks. 



From Cheyenne to Denver we examined with some care the mines about 

 the sources of the Cache a la PoudreEiver and the coal mines at South 

 Boulder. From Denver we visited the silver mines at Georgetown, and 

 the gold mines of Central City, thence to the Middle Park, where we 

 found much of interest geologically. We then returned to Denver and 

 pursued our way southward, passed the " divide"' to Colorado City, Soda 

 Springs, Canon City, Spanish Peaks, Eaton Hills, Fort Union, Mora 

 Yalley, Santa Fe, Placiere Mountains, &c. Along this route the 

 scenery was grand beyond description. At Colorado City there is an 

 area of about ten miles square that contains more material of geological 

 interest than any other area of equal extent that I have seen in the 

 west. 



The coal formation along the base of the mountains was studied with 

 great interest. With these coal beds are associated valuable deposits 

 of brown iron ore. The coal and iron deposits of the Eaton Hills extend 

 from the Spanish Peaks to Maxwell's, and the supply of both is quite 

 inexhaustible and of excellent quality. The future influence of these 

 two important minerals at this locality, on the success of a Pacific rail- 

 road, cannot be over-estimated. It is believed that the coal and iron 

 mines of the Eaton Hills will be of far more value to the country than 

 all the mines of precious metals in that district. 



The next locality for coal was at the Placiere Mountains. In one 

 locality here, the coal has been changed into anthracite by the eruption 

 of a basaltic dike, the igneous material of which had poured over the coal 

 strata. Vast quantities of brown iron ore are associated with this coal, 

 and magnetic iron ore is found in the gneissoid rocks of the mountain. 

 The gold mines here are very rich and are now wrought upon a true 

 scientific plan. 



From Santa Fe we proceeded up the Eio Grande through the San 

 Luis Valley, Poncho Pass, Arkansas Valley, through the South Park to 

 Denver again. We could only give a glance at the salt springs and 

 gold mines of the South Park, but we gathered much valuable informa- 

 tion in regard to this interesting region. To the geologist Colorado is 

 almost encyclopedic in its character, containing within its borders 

 nearly every variety of geological formation. The portion of the 

 country examined by ine this summer, comprises a belt about five hun- 

 dred and fifty miles in length from north to south, and almost two 

 hundred in width from east to west. 



The collections in all departments are very extensive and valuable, 

 comprising geological specimens, fossils, minerals, plants, birds, quadru- 

 peds, reptiles, and insects, all of which are to be arranged and classified 

 in the museum of the Smithsonian Institution according to a law of Con- 

 gress. 



My report, herewith transmitted, has been written under circum- 

 stances of great pressure at odd moments, in traveling from point to 

 point, or in camp after the labors of the day were completed, far away 

 from books or any opportunities for careful elaboration. It may there- 

 fore be regarded as little more than a transcript of my field-notes. 



Accompanying my own report will be found those of my assistants. 

 Mr. Persifer Frazer, jr., on the mining resources of the route passed over, 

 and Mr. Cyrus Thomas on the agricultural resources. I regard these 

 reports as of great practical value to the country. 



I take this opportunity of tendering my thanks to all of my assistants 

 for their cordial co-operation throughout the entire survey. The reports 

 of Messrs. Thomas and Frazer will speak for themselves. Mr. Elliott, 



