11 APPENDIX. 



The party climbed Pike's Peak, and, standing on its summit, 

 the district of country just described — South Park with its moun- 

 tain walls, its interior ranges, its deep valleys, its wild gorges, 

 its silver rivers and its crystal lakes, was all before them in one 

 grand view. In such a field the young men were instructed in 

 determining latitudes and longitudes, in determining relative 

 positions by triangulation, and in delineating the more important 

 topographic features. 



But mountains and valleys have something more than positions 

 and magnitudes to interest the student of nature — they have 

 structure ; and in this structure are revealed the great facts of 

 geology relating to displacement, degradation, sedimentation, 

 metamorphisra, and extravasation; and the field of study pi'e- 

 sented many interesting facts in each of these categories of phe- 

 nomena. The great ranges stood before them to attest to the 

 displacement or corrugation of the Earth's surface in mountain 

 wrinkles, and these mountains are seen to be but residuary frag- 

 ments of upheaved masses as plainly giving evidence of degra- 

 dation as they do of displacement; while the methods of degra- 

 dation by the wash of rains, by the sapping of clifts, by the 

 corrosion of water channels, and by the sculpture of ice, could 

 be studied on every hand. 



To Marvine, the summer's study was rich in results. He 

 learned that a mountain was more than a mountain, that it was 

 a fragment of earth's history. 



In the summer of 1870 Mr. Marvine was appointed assistant 

 geologist to attend the celebrated Santo Domingo Expedition, 

 and on his ^return he prepared a brief report on the economic 

 geology of some portions of that island which he visited. This 

 was published with the report of the Commission of Inquiry to 

 Santo Domingo by authority of Congress. It was a special and 

 brief study, and contains little of general interest to the geologist. 



In IStl he received an appointment as astronomer to the 

 Wheeler Expedition, in which capacity he served for several 

 months, and then continued several months longer as geologist. 

 His report on the geology of a district of country through which 

 he passed, embraced in southern Nevada, northwestern Arizona, 

 and southern California, has lately been published as one of the 

 papers in "Volume III. of the United States Engineer Reports 

 of the Explorations and Surveys west of the 100th Meridian, 

 Lieut. George M. Wheeler in charge. The region of country 

 studied by Mr. Marvine during these months of field service was 

 one of great complexity. On one side of his general route of 

 travel an extensive series of sedimentary formations are revealed, 

 embracing Tertiary, Mesozoic, and Paleozoic groups; on the 

 other, low mountain ranges are seen rising from a desert sea of 

 sand, the ranges being composed of more ancient sediments and 

 schists. The former is a portion of the Plateau Province, the 



(54) 



