Some Petrified Wood from the Specimen Ridge Area of Yellowstone National Park
1954; University of Notre Dame; Volume: 51; Issue: 2 Linguagem: Inglês
10.2307/2422124
ISSN1938-4238
Autores Tópico(s)Plant and animal studies
ResumoIn Yellowstone National Park practically all exposed rock formations are igneous or metamorphic consisting mostly of ash, obsidian and basalt. The central sector is made up of plateau country which though 7,000 to 8,500 feet above sea level, is nearly completely surrounded by mountain ranges rising 2,000 to 4,000 feet above it. The lava masses of Specimen Ridge in the Lamar River region are evidences of their volcanic origin and are considered by geologists to have been ejected from ancestral Mount Washburn during the early part of the Miocene or late Eocene. Specimen Ridge cliffs which outcrop 2,000 feet above the plateau extend for 20 miles along the Lamar River and include strata wihch contain some of the most remarkable petrified trees in the park. Many superposed layers of upright petrified trunks (not less than 15 according to Knowlton [18993) appear to indicate that in past geologic time a succession of forests flourished only to be repeatedly covered with volcanic ash and lava. The great wealth of extinct plants of the Lamar River region must have astonished the early explorers and though reference to the area is first made by the early naturalist, W. H. Holmes (Hayden, 1873), no extended studies of the fossilized wood were made before 1899, when Professor Knowlton published his monograph The Fossil Flora of Yellowstone National Park. Fossil wood specimens which Knowlton collected from the Specimen Ridge area of the park form the main body of material for anatomical reports in his monograph (1899). However, he collected plant fossils at sites other than Specimen Ridge, some of which he later investigated. Conard (1933) discussed Pityoxylon amethystinumi Knowlton, and, in the same year, Read investigated some fossil woods of Specimen Ridge and described those which he identified as Pinus baumani Read, Pinus fallax (Felix) Read, Cupressinoxylon lamarense Read, and Sequoia magnifica Knowlton. In 1939, Andrews reported on anatomical details of several collections of fossil wood from Yellowstone National Park with particular reference to the fossil forest of the north-west corner of the park known as the Gallatin region. Geologically, this area is similar to Specimen Ridge. Andrews redescribed Sequoia magnifica Knowlton, Cupressinoxylon lamarense Read and Pityoxylon
Referência(s)