438 C. K. LEITH 



Atlantic coast of pre-Cambrian and later age. He finds a striking 

 predominance of biotite granites and gneisses. 



Kemp, 1 in connection with a description of the magnetite deposits 

 of the Adirondacks of New York, publishes a geological map of por- 

 tions of Elizabethtown and Westport townships in Essex county, show- 

 ing the distribution of the pre-Cambrian magnetite-bearing gabbros, 

 the gneisses, and the limestones. No point in addition to those given 

 in previous reports appears. 



Merrill 2 gives a brief summary account of the geological forma- 

 tions of New York, including the pre-Cambrian of the Adirondack 

 area and of the southeastern part of the state. Accompanying the 

 report is a relief map showing the outlines of the geological forma- 

 tions. 



Cushing 3 describes an augite-syenite-gneiss near Loon Lake in the 

 Adirondacks. It is nearly related to the anorthosites in age, inasmuch 

 as it is intrusive in the Grenville series, but it is much older than the 

 pre-Potsdam diabases of the region. A study of the relations of the 

 syenites and anorthosites indicates that the syenites are in part a result 

 of differentiation in the anorthosite magma after reaching its place of 

 final cooling, and in part are somewhat later in date. 4 



Smyth 5 summarizes his ideas to date on the geology of the Adiron- 

 dacks. Gneisses, limestone, and gabbro are the principal rocks. 

 From studies in the western Adirondacks it is certain that some of the 

 gneisses are of igneous origin, being granites syenites, gabbros, etc., 

 which have been modified by metamoiphism ; while others, with equal 

 certainty, are altered sediments. But by far the larger part of the 

 gneisses have as yet received no careful study. The limestones are 

 certainly sedimentary. Their relations to the gneisses are in doubt, 

 but some parts of the gneisses are certainly younger than the limestones, 



1 The Titaniferous Iron Ores of the Adirondacks, by J. F. Kemp : Nineteenth 

 Ann. Rept. U. S. Geol. Surv., 1897-8, Part 3, 1899, PP- 377~422. With geological map. 



2 A Guide to the Study of the Collections of the New York State Museum, by F. 

 J. H. Merrill : Ball. N. Y. State Museum, Vol. IV, No. 19, 1898, pp. 109-262 ; with 

 geological map. 



3 Augite-Syenite-Gneiss near Loon Lake, New York, by H. P. Cushing : Bull. 

 Geol. Soc. of Am., Vol. X, 1899, pp. 177-192. 



4 The anorthosites are a part of the great gabbro mass which forms the core of 

 the Adirondacks intruding pre-Cambrian sedimentary and igneous gneisses. 



s Geology of the Adirondack Region, by C. H. Smyth, Jr.: Appalachia, Vol. IX, 

 No. I, May 1899. 



