PRE-CAMBRIAN NORTH AMERICAN LITERATUKE 367 
the intrusions as in several more or less parallel ranges, with remnants of the 
other rocks in the valleys between them and on the flanks is taken as a whole. 
The limestones and the associated rocks always occur in depressions, the 
resistant ridges consisting of the harder gneiss or anorthosite. The former form 
sections as broad as t1ooo feet, in which the limestone strata are, however, 
less than half, and the true thickness of which is difficult to determine because 
of the varying dips, schistosity, and possibility of faults. The white lime- 
stones are coarsely crystalline, usually graphitic, and often include silicates, 
from little scales to large bunches. At Keene Center, in the heart of the 
Adirondacks, is a white limestone and schist belt which contains magnetic 
iron ore, and is overlain by garnetiferous and pyroxenic schists, or pyroxenic 
granulite, the relations indicating that the latter is a gneissic rock interbedded 
with the limestone. 
There is no marked break to be detected anywhere between the gneiss 
and the overlying limestone. Apparently the whole is a continuous series 
of strata, which are analogous in appearancé with those of the Grenville 
series of Canada. It therefore does not appear certain that in the eastern 
Adirondack region are any rocks older than this series. The extent and per- 
sistence of the limestones and schists gives ground for believing that the 
series was a set of calcareous sediments and sandstones which have been 
metamorphosed and intruded by the anorthosites. 
Kemp" describes the titaniferous iron ores of the Adironacks. These 
occur in the gabbros. The ores are regarded as segregations from the igneous 
magma formed during the process of cooling and crystallization. 
Kemp and Marsters’ give the field occurrence and microscopical charac- 
ters of the trap dikes of the Lake Champlain region. The dikes are found 
to be bostonites, diabases, camptonites, fourchite, and monchiquite. 
Sears’ gives a description of each of the rocks of Essex county, Massa- 
chusetts. These comprise plutonic rocks, volcanic rocks, Archean rocks, and 
various metamorphosed sedimentary rocks of Paleozoic age. 
Emerson‘ gives an outline of the geology of the Green Mountain region 
in Massachusetts. The Algonkian rocks comprise the Washington gneiss, 
Tyringham gneiss, East Lee gneiss, Hinsdale limestone, and Hinsdale gneiss. 
*The Titaniferous Iron Ores of the Adirondacks, by J. F. Kemp, Abstract in 
Bull. Geol. Soc. Am., Vol]. VII., 1895, p. 15. 
The Trap Dikes of the Lake Champlain Region, by J. F. Kemp and F. V. 
MARSTERS, Bull. 107, U.S. G.S. With map. Washington, 1893. 
* Report on the Geology of Essex County, Massachusetts, to accompany map, by 
JOHN H. Sears, Bull. Essex Inst., Vol. XXVI., 1894, pp. 118-139. 
‘Geol. Atlas of the U.S., Hawley Sheet, Preliminary Edition, by B. K. EMERSON. 
U.S. Geol. Sur. Washington, 1894, 
