The Taconic or Lower Cambrian. — WincheU. 299 
whole region has very generally been mapped as Laurentian, 
following the original designation of Logan and the New 
York survey. Dr. Emmons was the first to call attention to 
the later date of the "hypersthene rock." He says:* 
"We know that the Hudson River series [i. e. what is now 
considered the Georgia slates of the Taconic. — N. H. W.] is 
distributed along the eastern base, or northeastern termina- 
tion of some of these ranges; an event which may have hap- 
pened very soon after their deposition, or at a still later pe- 
riod." 
In 1876 Prof, James Hall dissented from the prevalent idea 
that the marbles of the Adirondacks were of Laurentian age. 
He recognized two non-conformable portions of the so-called 
Laurentian, in the Adirondacks, but he asserts distinctly that 
"the limestone of that neighborhood (Fort Henry and West- 
port) did not form a part of the lower Laurentian series of 
strata, but unconformably overlaid the upturned edges of the 
gneissic beds of that portion of the system. "f Neither does 
this limestone conform to the upper, or labradorite, portion 
of the system. The upper portion, being composed, in his 
idea, "of massive beds of labradorite rock," and other granite 
rock, both being of irruptive origin, would hardly be expected 
to conform to the limestone. In this respect the crystalline 
limestones of the Adirondacks furnish an exact parallel, in 
their structural relations with the basic eruptives, to the 
limestones at Stony Point and Rosetown, a part of the well- 
known Cortlandt series. 
The Adirondack gabbros, therefore, have to be made to con- 
form, in date, to two leading facts. 
1. Thej" are earlier than the Potsdam sandstone (at least 
the Olenus horizon) which lies upon the "hypersthene rock," 
according to Emmons and later observers. 
2. They are later than the marbles and quartzyte, the mar- 
bles and quartzyte having furnished Lower Cambrian fossils 
in several places in Vermont closely adjacent. 
Whether they are earlier than the Middle Cambrian, as well 
*G('ol. of New York, Second district, 1842, p. 2G7. 
fNote on tlie Geoiof,'icaI position of the serpentine limestone of nortii- 
ern New York, and an inquiry refrardin<; tlie relations of this iimt'stone 
to the Eozoon limestones of Canada. Am. .lour. Sei., {?>), xii, p. 298, 187(). 
