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Show 61 APPENDIX G1. REPORT ON THE GEOLOGY OF THAT PART OF NORTHWESTERN NEW MEXICO EXAMINED DURING THE FIELD- SEASON OF 1874, BY E. D. COPE, PALEONTOLOGIST AND GEOLOGIST. PHILADELPHIA, June 11,1875. SIR : The present report includes the results of the investigation of the stratigraphio geology of the part of New Mexico to which you assigned me for the field- season of 1874. The ground covered embraces the eastern slope of the Rocky Mountains from Pueblo to the Sangre de Cristo Pass, both sides of the Rio Grande Valley from that point to Algodones, and the Sierra Madre range and the country for fifty miles to the westward of it from the latitude of Tierra Auiarilla to that of the road from Santa Fo" to Fort Win gate. Little of novelty has been added from the two first- named regions, as they have been previously traversed by competent geologists; but the last- named area has remained up to the present time almost unknown. The analysis of the structure of the Sierra Madre range is believed to indicate that its elevation took place near the close of the period known as Cretaceous No. 4, and that the elevating force was more powerful at its southern extremity in New Mexico than along the middle portion of its line. Another important discovery is the lacustrine character of theTriassic beds, which form a part of the axis of the range, indicating the existence of extensive areas of dry land at that period, of which no portion is remainiug in the region examined by me, but which may be supposed to be represented by the Paleozoic beds farther south and west. A third important point is the determination that the plateau drained by the eastern tributaries of the San Juan River is composed of the sediment of an extensive lake of Eocene age, which was probably at one tihie of great extent, but whose deposits have been greatly reduced in extent through erosion. The boundaries of this lake to the west and south were determined. It is believed that additional light has been thrown on the question of the age of the Galisteo sandstone, and that its paleontology has decided defiuitely that of the Santa F6 marls. The first fossils discovered in the " Trias " of the Rocky Mountains have enabled me to reach more definite conclusions as to its position in the scale of periods. I remain, with regard, E. D. COPE, Geologist and Paleontologist, Lieut. GEORGE M. WHEELER, Corps of Engineers. CONTENTS. Page. INTRODUCTION 61 CHAP. I- The geology of the eastern slope of the Rocky Mountains 62 CHAP. II- The valley of the Rio Grande to SantaFe* 64 CHAP. Ill- The vertebrate fossils of the Santa Fe* marls 68 CHAP. IV- The valley of the Rio Grande from Santa Fe* to the Zandia Mountains. 76 CHAP. V- The Sierra Madre and its western slope 78 CHAP. VI- The Eocene plateau 88 FINIS 97 INTRODUCTORY. The route pursued by the party to whom the duty of determining the geognostic character of the country was assigned is the following: Leaving Pueblo, it took the mam road southward for about thirty miles, to Howard's, on the Huerfano Creek. From this point its course was southwest, via Badito, and across the mountain- range at the Sangre de Cristo Pass to Fort Garland, in the valley of the Rio Grande. We then turned toward the south and followed the road on the east side of the Rio Grande one hundred and twenty- five miles, to Santa Fe\ Side- excursions were made to the east a short distance south of the Picons Mountains, and the west to El Rito, across the country, between the Rio Grande and the Rio Chama; also, to the Jeraez Mountains. The geological examinations were extended to the Zandia Mountains, forty miles south of Santa Fe*. The exploration to the west of the Rio Grande left that river at the mouth of the Rio Chama, and followed its course as far as the month of the Cafiou Canjelon, a distance of about thirty miles. The direction then pursued was north and northwest for thirty miles, reaching the Chama River again at Los Ojos. From this point the party followed |
