Davis.] 
318 
f Nov. 18. 
emergence required to unite them with the mainland. Is it not, 
moreover, possible that part of the present depth between the 
islands is due either to volcanic action, allowing subsidence, or to 
erosion among the islands by the active marine currents ? 
The following paper was read : 
THE CATSKILL DELTA IN THE POST-GLACIAL HUD- 
SON ESTUARY. 
BY WILLIAM MORRIS DAVIS. 
1. Introductory sketch of the history of the Hudson valley 
lowland : its Tertiary excavation in an elevated peneplain of Jur- 
assic-Cretaceous denudation ; the post-Tertiary trench cut in the 
Tertiary valley-lowland ; glacial action ; submergence of the trench 
into estuarine conditions and deposition of the Champlain clays ; 
subsequent elevation and partial trenching of the clays ; slight 
depression of the trench in the clays, letting the tide reach Troy, 
150 miles from New York. 
2. Merrill’s account of the deltas of lateral streams in the 
Hudson-Champlain estuary. 
3. The delta of the Catskill in the Hudson-Champlain estuary. 
The Cobble-field near Cairo ; the smaller delta of the Potuck ; the 
extension of the sands over the clays about Leeds. 
4. The terracing of the sands and clays. Variation in the 
width of the present flood-plain ; control of its level by the Cor- 
niferous ledge at Leeds. Preglacial course of the Catskill. 
5. Review. 
1. Introductory Sketch of the History of the Hudson 
Valley. An examination of a general section across the Hudson 
valley in the neighborhood of the Catskill mountains discloses 
traces, more or less distinct, of several stages in its history. It is 
not a constructional valley, like the so-called valley of California, 
a great trough between lateral upheavals ; the Hudson valley is 
a true valley of denudation. The general valley lowland, CD, fig. 
1, some twenty or thirty miles broad, diversified by subordinate 
ridges and stream courses, lies at a general elevation of 150 to 
400 feet above sea-level; it is excavated in an ancient upland, 
AB, whose altitude is indicated by the high levels of its remnants 
in the Highlands of the Hudson, and in the rolling surfaces of 
moderate relief high up among the Catskill mountains. Before 
the valley lowland was excavated, I think that these remnants 
