Geology topics
Clyde P. Ross
Publications and source records attributed to Clyde P. Ross.
Paleozoic seas of central Idaho
Some recent paleogeographic maps indicate that central Idaho was part of a major geosyncline throughout Paleozoic time. This concept, apparently based on thick marine accumulations far apart on the margins of the region, is inconsistent with field data. Within the area of the Idaho batholith, Permian(?) volcanic rocks rest either on batholithic rocks or on the Belt Series. The Belt Series rocks have furnished the xenoliths in the batholith. To the west upper Paleozoic and Mesozoic strata are invaded. Along the eastern margin, south of lat. 45°, thick Paleozoic strata are intruded by the batholith. These locally exceed 30,000 feet in thickness and thin eastward. They have many variations. Those close to the batholith, especially those high in the sequence, are regarded as of near-shore origin. The Paleozoic strata in southeastern Idaho , more than 17,000 feet thick, are broadly similar except that Cambrian strata there are thicker and more widespread. The part of central Idaho north of the vicinity of lat. 45° has no known Paleozoic strata. Northern Idaho has only a few outcrops of beds of Cambrian age. The differences in thickness and character between Paleozoic strata in south- central and southeastern Idaho and those in western Montana and Wyoming (less than 7500 feet thick) suggest a hinge line near the eastern boundary between Idaho and Montana with a shelf to the east and a trough to the west. In south- central Idaho this trough had a maximum width of 90 miles and a western shore roughly at the east margin of the batholith. This trough wedged out northward a little beyond lat. 45°. Thus the area of the present Idaho batholith has been a positive block since Precambrian time, comparable to but apparently of longer duration than the geanticline in northern Nevada. Any invasion of the positive block in Idaho by marine waters during the Paleozoic was local and brief, except perhaps along the western border. Uncertain correlations within the area of the batholith leave open the possibility of some deposition there early in Paleozoic time.
The rocks and fossils of Glacier National Park: The story of their origin and history
The story of Glacier National Park begins about 500 million years ago, at a time when there were no mountains in the region - only a vast, exceedingly shallow sea, bordered by desolate plains. The sand, clay, and mud, in part very limy, that were laid down in this sea eventually hardened into the rocks that are now known as the Belt series. These are the principal rocks in the park. Scattered through these rocks are crinkled, limy masses of many forms, the remains of deposits made by colonies of algae. After the Belt series was laid down, successive seas slowly advanced and retreated through long ages across what is now Glacier National Park, burying the Belt rocks under younger ones. After another very long time, a gentle uplift, the forerunner of later events, brought this part of the continent above the reach of sea water for the last time. Much later, some 50 million years ago, the disturbance became far more intense. To climax this upheaval, a mass of rock thousands of feet thick and hundreds of miles long was shoved eastward for 35 miles or more. This tremendous dislocation, well exposed along the eastern boundary of the park, is known as the Lewis overthrust. When the rocks of the region emerged from the sea they began to be attacked by erosion. As successive periods of crustal movement and erosion continued, the younger rocks were slowly stripped off the Belt series and sculpture of the latter by weather and water shaped the early Rocky Mountains. The final episode in the park's geologic past was the ice age, beginning about a million years ago. Repeated advances and retreats of the great glaciers in the high valleys accentuated the mountain terrain and developed the scenic grandeur that is now Glacier National Park. One may say that the park is still in the ice age, for some glaciers still exist. The present report, companion to two more technical reports on the region, informally presents the story of the park's development through past eras for readers without geologic training. Many places worth visiting are cited in the text, and a shaded relief map is provided to help find them.
Geology of Glacier National Park and the Flathead Region, Northwestern Montana
This report summarizes available data on two adjacent and partly overlapping regions in northwestern Montana. The first of these is Glacier National Park plus small areas east and west of the park. The second is here called, for convenience, the Flathead region; it embraces the mountains from the southern tip of Glacier Park to latitude 48 deg north and between the Great Plains on the east and Flathead Valley on the west. The fieldwork under the direction of the writer was done in 1948, 1949, 1950, and 1951, with some work in 1952 and 1953. The two regions together include parts of the Swan, Flathead, Livingstone, and Lewis Ranges. They are drained largely by branches of the Flathead River. On the east and north, however, they are penetrated by tributaries of the Missouri River and in addition by streams that flow into Canada. Roads and highways reach the borders of the regions; but there are few roads in the regions and only two highways cross them. The principal economic value of the assemblage of mountains described in the present report is as a collecting ground for snow to furnish the water used in the surrounding lowlands and as a scenic and wildlife recreation area. A few metallic deposits and lignitic coal beds are known, but these have not proved to be important and cannot, as far as can now be judged, be expected to become so. No oil except minor seeps has yet been found, and most parts of the two regions covered do not appear geologically favorable to the presence of oil in commercial quantities. The high, Hungry Horse Dam on which construction was in progress during the fieldwork now floods part of the Flathead region and will greatly influence the future of that region. The rocks range in age from Precambrian to Recent. The thickest units belong to the Belt series of Precambrian age, and special attention was paid to them. As a result, it is clear that at least the upper part of the series shows marked lateral changes within short distances. This fact introduces complexities into stratigraphic correlation and should be remembered wherever the series is studied. The stromatolites, or fossil algae, in the Belt series, although still imperfectly understood, give clues with respect to problems of ecology and stratigraphy. The subdivisions of the Belt series within the areas covered by the present report are, in ascending order, Altyn limestone, Appekunny argillite, Grinnell argillite, Siyeh limestone, and Missoula group. Local subdivisions of the Missoula group are possible in certain areas, and all the units just named are expected to be subdivided when detailed studies are undertaken. In the Glacier National Park and Flathead regions together, it is probable that between 25,000 and 30,000 feet of beds belonging to the Belt series, possibly more, are present. These consist largely of quartzitic argillite, quartzite, and carbonate rocks, mostly dolomitic. Small gabbroic and diabasic intrusive bodies and, at one horizon, basaltic lava are associated with the Belt series. Above the Belt series is a thick sequence of Cambrian, Devonian, and Carboniferous strata, in which limestone is dominant, followed by strata of Jurassic and Cretaceous age, largely limestone and shale and partly of terrestrial origin. Slightly consolidated gravel, sand, and silt of Tertiary age are preserved in some valleys and as erosional remnants on the plains close to the mountain border. Pleistocene and Recent glacial and fluviatile deposits are plentiful in mountain valleys and on the plains east of the mountains. Sufficient crustal movements took place during the latter part of Belt time to produce tension cracks that permitted some intrusion and related extrusion to occur. Broad crustal warping probably took place at intervals during the Paleozoic era, but these successive movements left little record other than the absence of sedimentary rock units that might otherwise have been deposited. The same can be said of much of the Me
The quicksilver deposits of the Terlingua region, Texas
Texas is second among quicksilver-producing States because of the Terlingua region, in the Big Bend of the Rio Grande. This region contains Cretaceous strata, largely calcareous, which grade upward into Tertiary volcanics, locally without break. The strata are cut by numerous intrusions, largely alkalic, and are extensively folded and faulted.Many of the lodes are near the base of the impervious Del Rio clay, some at higher horizons, and a few in intrusive masses. The solutions penetrated only along open passageways, such as major fractures or joints in zones of tension, and, especially at horizons above the Del Rio, in fractures related to fault zones.The quicksilver is believed to have been brought in by alkali sulphide solutions. Most other constituents that may once have been present in the solutions had been separated earlier. Precipitation resulted largely from mingling with groundwater. The comparatively low temperature and pressure at the shallow levels where groundwater was present aided the precipitation. As the then-existing zone of groundwater circulation has since been partly exposed by erosion, the lodes are necessarily rather close to the present surface. The gangue minerals, particularly the calcite, are believed to have been derived mainly from the sedimentary rocks with some addition of material from deep sources. The relation of the widespread bitumen to genesis is puzzling here, as in many other quicksilver deposits. Weathering is of slight economic importance. Many minerals that resemble supergene products, including the quicksilver chlorides, are thought to have resulted here from original deposition within the zone of vadose water.
Geology and ore deposits of the Casto quadrangle, Idaho
The study of the Casto quadrangle was undertaken as the first item in a project to obtain more thorough knowledge of the general geology of southcentral Idaho on which to base study of the ore deposits of t he region. The quadrangle conta ins fragmentary exposures of Algonkian and Paleozoic sedimentary rocks, extensive deposits of old volcanic strata, presumably Permian, not heretofore recognized in this part of Idaho, and a thick succession of Oligocene(?) lava and pyroclastic rocks. The Idaho batholith and its satellites extend into the quadrangle, and in addition there a re large masses of Tertiary granitic rock, not previously distinguished in Idaho, and many Tertiary dikes, some of which are genetically associated with contact-metamorphic deposits. The area contains injection gneiss of complex origin, largely related to the Idaho batholith but in part resulting from injection by ~he Tertiary granitic rocks under relatively light load. Orogenic movement took place in Algonkian, Paleozoic, and Tertiary time. There is a summit peneplain or par tial peneplain of Tertiary, perhaps Pliocene age, and the erosional history since its elevation has been complex. The ore deposits include lodes and placers. The lodes are related to both the Idaho batholith and the Tert iary intrusive rocks and have yielded gold and copper ore of a total value of about 1,000,000. Placers, largely formed in an interglacial inter val, have yielded about an equal amount. There has been some prospecting but almost no production since 1916.