528 C. K. LEITH 
Cushing* argues the existence of pre-Cambrian as well as post- 
Ordovician dikes in the Adirondacks and along Lake Champlain, offer- 
ing the following reasons: (1) A much larger number of dikes occur 
in the pre-Cambrian than in the Paleozoic rocks. (2) A great propor- 
tion of the dikes are of diabase, while diabase rocks are not found 
outside of the pre-Cambrian areas. (3) Along the line of contact of 
the Potsdam with the older rocks north of the Adirondacks, the plen- 
tiful diabase dikes in the older rocks are apparently cut off by the 
Potsdam. 
White’ describes and maps the geology of Essex and Willsboro’ 
townships, Essex county, N. Y. The Archean rocks of the townships 
comprise the following: (1) Labradorite rocks, gabbros, norites, and 
anorthosites, occupying the western half ot the area, west of the 
Boquet River ; (2) the metamorphic crystalline limestones and ophical- 
cites in the northeastern part of the area on Willsboro’ Bay, and in the 
southeastern part of the area on the ridge of Split Rock Point; (3) 
gneisses and granites, chiefly on Split Rock Point. Following Adams,3 
all of these rocks are classed as Norian or Upper Laurentian. 
Kemp‘ describes the geology of Essex county, N. Y. The pre- 
Cambrian succession in this county is as follows: (1) A gneissic 
series consisting of red and gray orthoclase gneisses, usually lam- 
inated, but at times rather massive. In these gneisses are the work- 
able iron ores of the Adirondacks. (2) Apparently resting on (1), 
a series of crystalline limestones, ophicalcites, black hornblendic 
pyroxenic schists, and thinly laminated garnetiferous gneiss. Pegmatite 
veins are a frequent associate of these rocks. (3) A series of rocks of 
the gabbro family, ranging from aggregates of labradorite through 
On the existence of pre-Cambrian and post-Ordovician ‘trap dikes in the 
Adirondacks, by H. P. CusHine: Trans. N. Y. Acad. Sci., Vol. 15, 1896, pp. 248— 
252. 
2 The geology of Essex and Willsboro’ townships, Essex county, N. Y., by T. 
G. WHITE: Trans. N. Y. Acad. Sci., Vol. 13, 1894, pp. 214-233, Pls. VI and VII. 
3Ueber das Norian oder Ober-Laurentian von Canada, F. D. ADAMS: Neues 
Jahrb., B. B. VIII, p. 423. 
4J. F. Kemp: Geology of Essex county (preliminary). Report of State Geolo- 
gist of New York for 1893, pp. 433-472. See also The Geology of Moriah and West- 
port townships, Essex county, N. Y. Bull. N. Y. State Museum, Vol. 3, 1895, pp. 325 
—351. With a geological map. 
