Page:The Journal of geology (IA journalofgeology11893univ).pdf/403

to work against this obstacle, abstracted its head waters and the gap was abandoned. The accompanying diagrams may make this easier to understand. Figure 2 is a cross-section of the faulted monocline, R showing the position of the river along the foot of the fault cliff. The line B L represents the surface of the country after baseleveling, the trap outcrops forming low hills (much exaggerated in the diagram). Figure 3 shows the dislocated trap sheets, the fault line and the winding course of the river, which has abandoned the fault line except where it passes between the low trap hills. Here the country is at baselevel. Figure 4 represents the region after the elevation and resulting erosion. The trap ridges have become more pro-

Figures 2-4.

nounced, and have migrated eastward in the direction of the dip. The river has been slowly let down upon the northern one from the sandstone at point G and has there cut into the solid trap.

The transverse notch of Cook's Gap, already described, was probably located in a somewhat similar manner, but the case is not so clear as at Tariffville.

Gravel terraces of the Farmington. A consideration of some facts concerning the height and slope of the terraces along this part of the river may give a clue to the answer to our question. One-half a mile east of Tariffville and east of the trap ridge, the highest terrace is 210 to 215 feet. Half a mile south of the same place but west of the ridge the height is 275 feet.^[1] The