The oblique trend of the coast would be even more pronounced but for a comparatively modern crustal movement, causing a depression in the northeast, with a resulting encroachment of the sea upon the land, and an elevation in the south-west, with a resulting advance of the land upon the sea.
The chief element of uncertainty as to the largest features of the relief of the earth's crust is due to the unexplored area in the Arctic region and the larger regions of the Antarctic, of which Crustal we know nothing.
The dominant forms result from crustal movements, the subsidiary from secondary reactions o during the action of the primitive forms on mobile distri butions.
The oblique trend of the coast would be even more pronounced but for a comparatively modern crustal movement, causing a depression in the northeast, with a resulting encroachment of the sea upon the land, and an elevation.
Trend to crustal deformations which in very early geological time gave a beginning to what later came to be the Appalachian mountain system; but this system had Its climax of deformation so long ago (probably in Permian time) that it has since then been very generally reduced to moderate or low relief, and owes its present altitude either to renewed elevations along the earlier lines or to the survival of the most resistant rocks as residual mountains.
The Upper Devonian was a period of marine retreat; the crustal disturbances of the Lower Devonian were renewed and great quartz-pebble beaches were formed on the rising shore lines, producing the West Coast Range conglomerates of Tasmania, and the similar rocks to the south-east of Mansfield in Victoria.
In this province, therefore, we find a part of one of those ancient mountain regions, initiated by crustal deformation, but reduced by long continued erosion to a peneplain of modern relief, with occasional surmounting monadnocks of moderate height not completely consumed during the peneplanation of the rest of the surface.
A broad, low crustal arch extends southward at the junction of the Atlantic and Gulf coastal plains; the emerged half of the arch, constitutes the visible lowland peninsula of Florida; the submerged half extends westward under the shallow Florida.
Arrange- Professor C. Lapworth has generalized the grand features meat of of crustal relief in a scheme of attractive simplicity.
The basins have been variously ascribed to glacial erosion, to obstruction of normal outlet valleys by barriers of glacial drift, and to crustal warping in connection with or independent of the presence of the glacial sheet.