liase of the Tdconlc or Lou'cr Co itihrifn). — WlticlieU. 159 
"). ("(Jiiylomcrale, firmly bedded upon tin- uiiderlyiim- Liiieiss. appar- 
eiitl}- fhaiigiiig to f^'iieiss in some places. 
These parts have all been found to contain the characteris- 
tic fossils of the Taconic or Lower Cambrian. Their age is 
no longer in question. The thickness of this series of strata 
is \QYy great, reaching more than twenty thousand feet. To- 
ward the south the}^ become crystalline and have been con- 
sidered, on lithological characters, as belonging to the Ar- 
chean. Thej*^ are all involved with the basic gabbros at 
Cortlandt, N. Y., and are converted into apparently massive 
eruptives, taking the various forms of dioryte, and quartzose 
granitoid rocks,* while at more remote points from the focus 
of igneous action the region is occupied by mica schists and 
gneisses, produced by a regional metamorphism of the same 
strata, as shown by Dana. The base of the Taconic, therefore, 
if the continuous areal tracing of these strata from Vermont 
to New York city by Prof. Dana was correct, is apt to be crys- 
talline and has been invaded by gabbros and associated basic 
eruptives, at least in the region of eastern New York south 
from Albany. The iron ore belt which is closely connected 
with the main limestone stratum in the same region, is another 
noteworthy' feature. Dr. Edward Hitchcock traced it out 
carefully in Vermont and represented it by a continuous color 
running into Massachusetts. Prof. Dana has followed it as 
far sou til as Dutchess county. 
A similar crystalline series is found in the Adirondacks, in- 
timately connected with the gabbros of that region. The 
Adirondacks are on the opposite side of the Hudson-Cham- 
plain valley and must be considered to have had a iiistory in 
some broad respects identical with the history of the eastern 
side. The eruptives here followed the 'I'aconic strata, as to 
date, and where they did iu)t effect their fusion tiiev rendercti 
them (irystailine over wide areas, jjroilucing a series <[uite 
different from tlie true Archean. Massive c|uartzytes and 
bedded gneisses are inchuhul in this later crystalline series, 
associated with marble, hematite iron ore, and conglomerates. 
In general the eruptive rocks not only are of the same kinds 
as those of the Cortlandt area, but they have the same rela- 
tions to the concerned elastics. They have broken through 
*(i. H. \Vii-M.\Ms. Am. .lour. Sri., (a) xxxv, pp. l;iS-f4S. ISSS. 
