The Triassic rocks are mainly red sandstones,—­often feldspathic, or arkose, with some conglomerates and shales.  Considering the large amount of feldspathic material in these rocks, do you infer that they were derived from the adjacent crystalline and metamorphic rocks of the oldland of Appalachia, or from the sedimentary Paleozoic rocks which had been folded into mountains during the Appalachian deformation?  If from the former, was the drainage of the northern Appalachian mountain region then, as now, eastward and southeastward toward the Atlantic?  The Triassic sandstones are voluminous, measuring at least a mile in thickness, and are largely of coarse waste.  What do you infer as to the height of the lands from which the waste was shed, or the direction of the oscillation which they were then undergoing?  In the southern basins, as about Richmond, Virginia, are valuable beds of coal; what was the physical geography of these areas when the coal was being formed?

Interbedded with the Triassic sandstones are contemporaneous lava beds which were fed from dikes.  Volcanic action, which had been remarkably absent in eastern North America during Paleozoic times, was well-marked in connection with the warping now in progress.  Thick intrusive sheets have also been driven in among the strata, as, for example, the sheet of the Palisades of the Hudson, described on page 269.

The present condition of the Triassic sandstones of the Connecticut valley is seen in Figure 315.  Were the beds laid in their present attitude?  What was the nature of the deformation which they have suffered?  When did the intrusion of lava sheets take place relative to the deformation?  What effect have these sheets on the present topography, and why?  Assuming that the Triassic deformation went on more rapidly than denudation, what was its effect on the topography of the time?  Are there any of its results remaining in the topography of to-day?  Do the Triassic areas now stand higher or lower than the surrounding country, and why?  How do the Triassic sandstones and shales compare in hardness with the igneous and metamorphic rocks about them?  The Jurassic strata are wanting over the Triassic areas and over all of eastern North America.  Was this region land or sea, an area of erosion or sedimentation, during the Jurassic period?  In New Jersey, Pennsylvania, and farther southwest the lowest strata of the next period, the Cretaceous, rest on the eroded edges of the earlier rocks.  The surface on which they lie is worn so even that we must believe that at the opening of the Cretaceous the oldland of Appalachia, including the Triassic areas, had been baseleveled at least near the coast.  When, therefore, did the deformation of the Triassic rocks occur?

Western north America.  Triassic strata infolded in the Sierra Nevada Mountains carry marine fossils and reach a thickness of nearly five thousand feet.  California was then under water, and the site of the Sierra was a subsiding trough slowly filling with waste from the Great Basin land to the east.