1894. | NEW YORK ACADEMY OF SCIENCES. 229 
plain are estuary formations of the same age as those along the 
Hudson Valley. Openings have been made in them at Platts- 
burg, Essex, and a few other localities.” The same writer men- 
tions that, while the clay is generally blue, the upper few feet 
weather to red, owing to an oxidation of the iron. 
Mr. Baldwin* considers that the clay plain which lies between 
the lake and the foot hills further north is due to the covering of 
Champlain clays and sands concealing the buried slopes. He 
traces the Pleistocene valley from Whitehall to Au Sable, with 
an accompanying map upon which his shore line of the ancient 
Champlain glacial lake follows around the sand hills above men- 
tioned very nearly as depicted in Emmons’ supposed Tertiary 
beaches. 
Mr. Warren Upham} has attributed the depression of the 
Champlain valley to the weight of ice at the close of the second 
glacial epoch. This admitted the sea to the lake basin, and was 
followed by glacial retrocession, with continued Sal taeirces of 
upper till and deep flood plains of gravel, sand and clay (strati- 
fied and modified drift). The latter were deposited in valleys 
which received the drainage from the glacial melting, during its 
rapid progress through the Champlain valley. Dr. F. J. H. Mer- 
rillf has traced the course of deposition first of the heavier sands, 
and then of the lighter silts which afforded clays, in similar cases 
in the adjacent Hudson River valley. 
THE DIKES. 
Dikes of light colored porphyry and dark basic diabase cut 
all the Paleozoic formations as well as the Archzean, and hence 
must have originated later than the Utica shale. Eighty-six 
dikes located in the two townships are enumerated in Appendix 
I. A further petrographic study of them is reserved for a future 
paper. The basic dikes are most abundant, although the lighter 
colored varieties occur in the same localities. The most abund- 
ant locality is along the western shore of Willsboro’ Bay, and in 
the Utica shale of Willsboro’ Point,as shownin Plate VI. The 
cliffs on the west side of the bay rise abruptly to a height of 
nearly two hundred feet, and the railroad cut which hugs a ledge 
about half way up the face affords a magnificent exposure of 
*S. PRENTISS BALDWIN: Pleistocene History of the Lake Champlain Valley. 
Amer. Geol. 1884; XI1I: 170 (Plate V.). 
+ WARREN UpHamM: A Review of the Quaternary Era; Am. Jour. Sci. 1891, 
XLI: 83. Also Bull. Geol. Soe. Am., I: 566; IL: 265; III: 484 and 508. See also 
Baron G. DE GEER: Amer. Geol. 1893, XI: 36; and Proc. Bos. Soc. Nat. Hist. 
1892, XXV: 454, with map of Pleistocene changes of level. 
t Postglacial History of the Hudson River Valley. A.J.S., iii. XLI: 460. 
