1880. | of the Atlantic States. 707 
strata must have extended on to the eastward? Opposite New 
York city fully three hundred feet of sandstone and slate is 
exposed beneath the trap, their broken edges forming the shore 
of the Hudson at Weehawken. It is to be remembered in this 
connection also, that these beds were off-shore deposits and had 
an inclination of fifteen degrees to the westward. 
Sixthly. If we could arrive at definite results in reference to the 
present rate of erosion of the Triassjc rocks, we could form more 
accurate conclusions as to the former thickness of this formation. 
We know, however, that the present waste, although the rocks 
are but little elevated above the sea, is very rapid. Composed of 
soft shale and sandstone, and highly inclined, these rocks present 
the most favorable conditions for rapid erosion; if these rocks 
have been exposed to subaerial denudation for a long time, it fol- 
lows that an mnene amount of material must have been 
removed. 
The present drainage of the country shows that the upheaval 
of the Triassic beds was extremely gradual, and hence that they 
have been exposed to denudation for ages. The Delaware, for 
instance, flows at right angles to the strike of the rocks, and has 
carved out a broad anticlinal valley, about thirty miles in length, 
through the shales, sandstone and trap sheets of the’ Triassic. 
From this we must conclude that the Delaware flowed eastward 
through this region before the rocks were upheaved, and that the 
elevation of the beds went on so slowly that the river was enabled 
to cut out its channel as fast as the rocks were brought within its 
reach. The Susquehanna, thé Potomac and other rivers to the 
south, also bear evidence to the slowness with which the Triassic 
rocks were elevated, and consequently to the great lapse of time 
during which they were exposed to subaerial erosion, The deep 
cañon-like valley of the Hudson, now partially filled, bears evi- 
dence of the same nature. No one who does not believe that the 
Surface of the earth has always been as we see it to-day, can 
resist the conclusion that the Triassic rocks must at one time 
have had a very great thickness. The problem of measuring the 
former extent and thickness of. the Triassic rocks in feet is far 
from being determined; we can only conclude from the above 
considerations, as the time has been long and the rate of erosion 
rapid, that their former thickness must have been very great, 
The material removed from the region separating the two Tri- 
