4 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



plex ecbelon-folds of the nortb, and the changes between — are shown 

 (Plate II) by cross- sections at seventeen points along the mountain-front. 

 A map to sliow the distribution of the Lignitic coal-openings, with rail- 

 roads, &c., is also given, and attention paid to what is at present known 

 concerning the usefulness of these coals. 



The mountains are composed of a great series of metamorphic schists, 

 gneisses, and granites of pre-Silurian age, (with minor masses of erupt- 

 ive rocks,) all thrown into a complex system of folds, which are very 

 difficult to trace on account of the absence of permanent features in any 

 one horizon ; metamori^hism so frequently obscuring what distinctive 

 features certain strata may possess for a little distance. A single, 

 indeed many, season's work, would be insufficient to unravel the i^roblems 

 in structure, but more especially in metamorphism, here presented. 

 Even such material as is here presented cannot be made fully available 

 nntil carefully plotted on the final map. In the mean while, how- 

 ever, Mr. Marvine has prepared a provisional geological map of the 

 eastern slope of the front range, where these rocks were best studied, 

 which shows their general structure, accompanying it with a brief chap- 

 ter on the more general j)heuomena here observed. 



The Sedimentary rocks of the Middle Park form the subject of Chap- 

 ter IV, their distribution being shown on the accompanying map, and 

 their structure by the five cross-sections on Plate III, together with 

 minor sections and figures. The relations between the geology and the 

 topography is particularly referred to. The more interesting geological 

 features here observed are : that the Cretaceous rocks seem to be the 

 oldest Sedimentaries, resting directly on the Archaean, a decided uncon- 

 Ibrmability of deposition between the Cretaceous and Lignitic formations, 

 proving that a small east and west anticlinal fold, which occurs along 

 the Lower Grand River in the Park, was formed at the close of the Cre- 

 taceous, and before the more extended Eocky Mountain uplift ; the 

 inclination of probably post-Tertiary lake-beds, pointing to a compara- 

 tively recent slight continuation of this uplift ; and interesting glacial 

 ]:)henomena. 



The energy and devotion to the work displayed by Mr. Marvine 

 merit the highest commendation, and the results so admirably brought 

 out in his report, as shown by the above short resume, are but the prom- 

 ise of the future. The map of the first district, prepared by Mr. Bech- 

 ler, with the assistance of Mr. Ladd, will be engraved the present sum- 

 mer, and will more than sustain the high reputation which he gained 

 by his labor in the Snake River district during the season of 1872. 



During the field-season of 1873, Henry Gannett was topographer in 

 charge of the Middle or South Park division. This party consisted, during 

 the greater part of the season, of eight men, Dr. A. C. Peale, division 

 geologist; W. Rush Taggart, assistant division geologist; Henry W. 

 Stuckle, assistant topographer; J. H. Batty, naturalist ; two packers; 

 and a cook. 



