570 W. M. DAVIS — DATES OF TOPOGRAPHIC FORMS. 



defined conditions lias been continued during the greater part of Tertiary 

 time, and thus the open Triassic lowland and the strong-featured valley from 

 Middletown to the sound are to be dated. The lower valley is relatively 

 narrow, as it is cut in hard crystalline rocks ; but in the Triassic belt, where 

 the rocks are weak, the valley has widened out to a lowland, although it is 

 no older there than in the crystallines. The wide lowland on the weak rocks 

 and the narrow valley in the hard rocks are both the work of the same cycle > 

 of development, and the waste from both has been carried away by the same 

 river. The marked differences of form in the two parts are due to the dif- 

 ference in the resistance of the rocks; not to any difference in the height of 

 the mass; not to any variation in the time of action ; not to any inequality 

 in the power of the controlling stream. The same contrast of form, due to 

 contrast of rock-resistance under conditions otherwise similar, is to be found 

 throughout the Atlantic slope. 



Tertiary Work in New^ York : the Hudson River. — Passing now to south- 

 eastern New York, we find in the Hudson a close parallel to the Con- 

 necticut. In the Highlands the Hudson has cut the finest gorge in the east, 

 ern United States; although sometimes spoken of as of great antiquity, it 

 is not so in a geological measure of time, being not more remote than the 

 Tertiary period. Up-stream from the Highlands there is broad lowland 

 stretching toward the Catskills, and including the areas that further to the 

 southwestward are separated by Kittatinny mountain into the great valley 

 and the Alleghany lowlands, but which here are nearly merged, on account 

 of the absence of the Medina sandstone. Throughout all the Hudson valley, 

 from the Highlands to Albany, there is nothing to indicate the height of the 

 mass in which the valley-lowland has been carved, but toward the south and 

 east lies the uplifted peneplain of the New York highlands and of Berk- 

 shire, while toward the west rises the hilly upland of the Catskills ; and in 

 presence of these witnesses it seems most likely that the surface from which 

 the present Hudson valley has been excavated was truly once a part of the 

 great lowland of Cretaceous times. If one stands on the Catskill mountain 

 front and looks eastward across the valley, this conclusion seems well nigh 

 incredible ; the excavation of the lowland from the Catskills to the Berkshire 

 plateau seems too great^a work for Tertiary time, but the arguments in favor 

 of it must in the end bring conviction of its truth, in spite of the enormous 

 destructive work that it requires. An indirect argument to the same end 

 is found in the course of the Hudson itself. If the river is followed down 

 from Albany to New York, as it may be in a delightful excursion on one 

 of the " day boats," the Highlands are encountered below Newburgh, where 

 they rise like a great wall across the course of the river, while the lowland 

 bears away to the southwest, continuing in that direction through the Kit- 

 tatinny valley of New Jersey and Pennsylvania, the Shenandoah valley of 



