MAKVINE.] 



GEOLOGY METAMORPIIIC EOCKS OF THE MOUNTAINS. 139 



of the metamorphism was unmistakable. Bisappearing beneath the 

 rocks of the plains it becomes impossible to tell how far the series and 

 its characters may continue in that direction. Where appearing through 

 the sedimentaries of the Middle Park and from beneath them along their 

 western border in the park range, their clearly metamorphic nature is 

 still present. Again covered with the sedimentaries, yet many hun- 

 dreds of miles to the south and west, where the canons chiseled by the 

 Colorado and its tributaries have penetrated the upper rocks, and on 

 beyond past the limits of the Colorado plateau, in the regions of Ari- 

 zona, jS'evada, and Utah that have been stripped of the sedimentaries, 

 rocks similar in character occur, indicating that the substratum of the 

 whole country is what is left of ancient and highly metamorphosed 

 series of rock formations. I^o special facts bearing on the equivalency 

 of the metamorphic series, as exposed in the front range of Colorado, to 

 any of the divisions of the Archaean rocks at the East, were observed. 



The prevalence of siliceous and granitic types recalls the descriptions 

 of Laurentian areas. But the presence of granites may only mean extent 

 of metamorphism and not necessarily a greater age. There may, indeed, 

 betherepresentativesof twoor more groups of the Archsean present, but a 

 strong impression was received that there was but one great conforma- 

 ble series of rocks, and that its characters might be quite peculiar to 

 the series and region in question. It will be impossible here to go into 

 any detailed lithological study of the series. Though, notwithstanding 

 the extended and rapid character of the exploration, much material was 

 gathered bearing on the subject, yet sufficient time for its elaboration 

 and study has not yet elapsed, and more complete results must be post- 

 poned for a final report. A few general results, however, can be offered. 

 Considering the extent and antiquity, the formation and the probable 

 mutations of its history, its lithological characters, as a whole, seem to 

 be remarkably simple and uniform. From quartzite through siliceous 

 and mica schists to very simple varieties of gneisses and granites, in 

 which the mica is wholly subordinate, and the feldspar mostly a tabular 

 and twined orthoclase, with possiblj^ one or two triclinic feldspars pres- 

 ent, and the list of rocks seems complete. Aside from an apparent 

 tendency at several points to the formation of iron garnets, hardly any 

 other accessory minerals were observed, while the syenitic element and 

 the more basic rocks generally were almost entirely wanting. This does 

 not refer, of course, to the occurrences of manj' minerals, some contain- 

 ing rare elements, in veins, nor to mere local rock occurrences, but to 

 the impressions received from the general and extended view of the 

 formation as a whole. 



The least metamorphosed rocks observed were quartzites, the purest 

 form of which were of clear milk-white or bluish color, excessively hard 

 and compact. Near the lower caiions of Coal and Ealston Creeks, where 

 the largest mass observed had been preserved from erosion, they passed 

 into a series of highly siliceous schists, in places very ferruginous, and 

 which may possibly yet be found to contain workable deposits of iron- 

 ore. They were here associated with siliceous mica schists finel}', com- 

 pactly, and evenly bedded or banded. Above very irregular schists 

 occurred, contorted and blotched, largely composed of lenticular-like 

 masses of white feldspathic and black or dirty-red micaceous material, 

 intercalated irregularly together, with garnetiferous schists. Gueissic 

 and granitic strata are frequent, while below a great granite mass occurs 

 with but remnants of bedding left, but which are apparently conforma- 

 ble with the series above. Both above and traced along the series more 



