1894. ] NEW YORK ACADEMY OF SCIENCES. 219 
galena in their possession, which could not have been trans- 
ported from any considerable distance. The Indians were in 
the habit of landing near the mountains * * * returning 
in a few hours laden with lead ore of the richest quality.” 
Mention should also be made of a vein of * garnet-resinite ” 
(colophonite), accompanied by tabular spar, garnet and pyrox- 
ene, in a trap dike in the Archzean near the lakes in northern 
Willsboro’, which was not visited last summer, but of which we 
have several records and analyses.* 
Granites and gneisses: The geology of these rocks on Split 
Rock Point is quite complex. The ridge, the end of the point 
and the isolated mass of Split Rock itself are of crystalline 
limestone, around which is a series of gneisses and granites, of 
varying texture, becoming more acidic as we go southward. 
Graphite is plentiful all through these gneisses and in the 
bunches of silicates, etc. (scapolite, pyrrhotite, sphene, horn- 
blende, phlogopite), in the limestone, especially along the con- 
tact. In the woods between the roadside and the north shore is 
a feldspathic vein in the gneiss. Numerous dikes also appear, 
as in the appended tabulation. The gneiss overlies the granite 
near the end of the point, but numerous cortortions of horn- 
blendie schists appear intermingled on the surface confusing the 
relations. Split Rock Point and Mountain both receive their 
names from the mass of rock at the tip of the point, isolated by 
a cleft, or “split,” fifteen or twenty feet wide, which is flooded 
at high-water periods. The island consists chiefly of crystal- 
line limestone with peculiarly contorted segregations of sili- 
cates, and schistose hornblendic bands (probably resulting from 
metamorphosed dikes), which so much resemble snakes that 
they are considered petrifications by the natives. The general 
geological features of Split Rock are set forth by Kemp and 
Marsters in Bulletin 107, U. S. Geol. Surv., p. 41. 
Pegmatite veins are common associates of the dikes in the 
Archean along Willsboro’ Bay, and also on the south side of 
Split Rock Point; in the latter locality they contain masses of 
graphite. 
CAMBRIAN (POTSDAM) QUARTZITE. 
The geographic distribution of the Potsdam terrane about the 
Adirondacks is delineated on the geological map of New York 
accompanying the final report in 1842, and in the large map by 
*W.C. Watson: Trans. N. Y. State Agri. Soc., XIII. (1853): 720. 
A. E. JEssup: Jour. Acad, Nat. Sci. Phila., II. (1821): 182. 
LARDNER VaNUXEM: Analysis of Table Spar from Willsboro’, same ref. 
L. C. Beok: Mineralogy of New York. p 326. 
H. SEYBERT: Am. Jour. Sci., Series 1, V.: 118. 
