206 The American Geologist. May, 1895 
but there is little or none in America. In the Archoan, or in 
other words, in the fitndamenlal comjilex which lies below the 
great non-conforniity, ma}' be seen a great series of basic eriip- 
tives. In general they are known as the "greenstones." They 
fade out into chlorite schists, to silky sericitic schists, and to 
clajr slates. They also become agglomerates and conglomer- 
ates, the pebbles of which cannot be referred to anj^ adjacent 
formation as their source.* This volcanic mass, in Minnesota, 
when it is compact and destitute of proof of sedimentary 
structure, rises to considerable altitude above the surround- 
ing country, forming a continuous ridge or range of low mount- 
ains, and has been named Xairit<hiirin. It is apparently the 
latest of the Archean formations. It is involved with the rest 
of the Archean in upheaval and pressure, and on it lies the 
base of the Taconic in the same non-conformable attitude as 
on the gneiss or granite of the other parts of the Archean. It 
is in this greenstone that occurs the hematite ore of the Ver- 
milion range. There are in addition to these greenstones 
many acid eruptives, such as granites and felsytes, the nature 
and origin of which need not be here considered. 
The Taconic basic eruptives are very difl'erent. They have 
not been subjected to the upheaval and shearing which the 
Archean eruptives have suffered. They are freshly crystalline, 
or beautifully amygdaloidal. They have been both effusive- 
eruptive and plutonic. They are as laccolites in the slates, 
making dikes and sills in the strata, and as surface flows and 
sedimentary ash.f Their date is positively later than the 
Archean and earlier than the Olenus horizon. They are of two 
distinct epochs, and they continued active during very long 
periods. They appear in the Taconic from the eastern part 
of the United States westward to the northern side of lake 
vSuperior and to the Arctic shores. In some places they have 
been considered Archean, in others Cambrian, in others they 
have been covered by a new mantle, an ambiguous and unne- 
cessary nomenclature. But in all cases they bear a lithologic 
stamp, or group of petrographic characters, by which they 
can be distinguished from the Archean, and in most cases 
*Comi);ire "The Origin of the Archean Greenstones" by the writer, in 
23d annual report of the Minnesota survey. 
fC.R. Van Hise, Bull. Geol. Soc. Am., vol. iv, p. 435, 1893. 
