584 THE JOURNAL OF GEOLOGY. 



about 150 feet above the water in the portions westward. The 

 streams in this region were revived and a terraced trough was cut 

 within the earlier Columbia trough. That this uplift was also 

 rapid is indicated by the steep sides of the trough, but the 

 emergence was not so long continued as the Post-Tertiary uplift, 

 for when base-level was reached the trough was widened only 

 about half as far. The general nature of this trough in the Wash- 

 ington region and eastward is shown in the third section in 

 figure 3. Farther northward the earlier Columbia terrace was 

 more widely degraded, owing to the somewhat increased amount 

 of uplift in that direction. During this epoch there was con- 

 siderable erosion in the Piedmont region, shown mainly in the 

 cutting of steep-sided inner gorges, and a general deepening of 

 the drainage ways. As the cutting reached base level a series of 

 wide terraces were cut in the vicinity of Washington, along the 

 Delaware valley and around southern New Jersey, which were 

 essentially continuous with those of the submerged region to the 

 east and south. During the uplift this submerged region received 

 the products of the degradation, and the coarse, cross-bedded 

 sands, shown at 3 in figure 3, are just what we should expect under 

 the conditions. 



The widening of the Inter-Columbia troughs was terminated 

 by general subsidence, during which the later Columbia deposits 

 were lain down under conditions almost precisely similar to those 

 of the earlier Columbia deposition ; first, the coarse basal beds, 

 and then the fine loams, with few scattered bowlders and frag- 

 ments. They were deposited on the lower terrace plains of the 

 depressions in the uplifted region, but to the eastward they were 

 laid down in open waters over the earlier Columbia deposits and 

 the intermediate deposit; 3 in figure 3. The later Columbia 

 waters extended across the Coastal Plain region in the larger 

 valleys and for some distance into the Piedmont region, but 

 their western limits are not definitely known. In figure 4 the 

 area of later Columbia submergence is represented, and some of 

 its relations are shown in section 3, figure 3. The later Col- 

 umbia terraces extend to the Great Falls in the Potomac, but the 



