| OCR Text |
Show xii GEOLOGY OF THE HIGH PLATEAUS. should be studied in detail, that the great structure lines, the faults and flexures, should be carefully traced, and the displacements determined quantitatively ; but the most important part of the investigation to be made was presented in the study of the volcanic formations, which are the chief characteristics of the group of High Plateaus. No systematic work had been done in this field. Our knowledge of it was chiefly confined to its geographic extent and to a general belief that an extensive series of volcanic rocks would be found, and that the subject was of great complexity. At this stage Capt. C. E. Dutton, of the Ordnance Corps, was induced to undertake the investigation. Three seasons were devoted by him to field labor, and the intervening months were chiefly given to laboratory study of the materials collected in the field. With great labor and skill the work has been accomplished, and its results are presented in this volume, which will be found to extend our knowledge of the geology of the United States and to be an important contribution to geologic philosophy. To a large extent the sedimentary region embraced in the survey of which this volume treats is destitute of vegetation and soil and its rocks are so naked that good sections are obtainable on every hand. Again, the region is dissected by deep canons. From both of these reasons the geology is plainly revealed. Every fault, every flexure, the relations of successive strata, unconformities, and all facts of structure are seen at once. But there are two sources of obscurity. First, some of the highest plateaus are covered with forests and vegetation. Second, the extravasated rocks are aggregated in a much more confused manner than the sedimentary beds, and greater labor and care is required in tracing them, and after the utmost care uncertainties and doubts remain. Thus it is that in describing the structural geology of the region the details of examination do not appear as in reports on regions of country less favorable to geologic examination. To a large extent, also, the details of structure are omitted from the text and appear in the graphic illustrations which accompany the report. It has been the policy of the survey to relieve its reports to the utmost extent of burdensome details of verbiage, by presenting them, as far as possible, through graphic methods to the eye. The early reconnaissance of the country was in part made by Mr. |
