GEOLOGICAL SURVEY OF THE TERRITORIES. 159 



theCoal group, probably Lower Tertiary or Upper Cretaceous. AtEvans- 

 toii we have the great coal-mines, which have been described to some 

 extent in my j)revious reports, and are still further described by Dr. 

 Peale in a subsequent portion of this report. The numerous species 

 of plants which were found above and below the coal-beds are described 

 in the report of Professor Lequereux on the fossil plants collected by 

 the expedition. I had intended to add some additional chapters, and a 

 final one, which should comprise a resume of the geology of the country 

 examined during the past season, but the time would not permit. It is 

 my purpose to press on with all the vigor possible to collect the facts 

 which shall establish the age of the diffierent formations of this portion 

 of the West -, more especially to ascertain the relation the coal-beds 

 sustain to the Cretaceous and Tertiary i)eriods. , 



NOTES TO CHAPTER IX. 



The following letter of Dn Drown conveys so much valuable informa- 

 tion in regard to the chemical character of the remarkable Soda Springs 

 at the base of Pike's Peak, Colorado, that I am glad to append it to this 

 chapter, for the purpose of comparison with the waters at Soda Springs, 

 on Bear Eiver. The letter is i)ublished bj^ permission of Dr. R. H. Lam- 

 born. The information is of greater interest to me, from the fact that 

 the springs were examined with some care by my i)arty in 1869, and 

 a short account of them was given in my report of the United States 

 Geological Survey of Colorado and New Mexico : 



Laboratory, 209 South Sixth Street, 



Philadelphia, November 11, 1871. 



Dear Sir : I take pleasure in transmitting to you the results of my 

 examination of the salts placed in my hands through the kindness of 

 yourself and Professor Persifor Frazer, jr. These salts were the residue 

 of evaporation of the water of the spring called the " Doctor," one of the 

 well-known gToup of mineral springs atthe foot of Pike's-Peak, Colorado, 

 now reached by the Denver and Rio Grande Railway; which springs, I 

 understand, now belong to the Fountain Colony, and are about to be im- 

 proved with a view to the utilization of their sanitary qualities. The sub- 

 stance submitted for analysis was obtained by Professor Frazer, jr., from 

 the spring in question when engaged on the mineralogical survey of C'olo- 

 rado in 1869, and was the result of the evaporation of a considerable 

 quantity of water. The means at hand for evaporation were so crude 

 that some substances, not properly belonging to the water as it comes 

 from the earth, have become mixed with the material used in my deter- 

 minations ; but their nature is such that I think they may be readily 

 eliminated, leaving the ultimate result quite accurate. 



The result of the analysis was as follows : 



Per cent. 



Organic matter 9. 33 



Sesquioxide of iron 4. 49 



Alumina 0. 87 



Silica and quartz 6. 10 



Lime 5. 64 



Magnesia 2. 57 



Potassium 4. 86 



Sodium 21. 60 



Oxygen by calculation 2. 87 



