300 The American Geologist. May, 1895 
as the Oletuis zone, there is not siiflicient evidence to warrant 
a judgment, although tliere is some evidence, which need not 
be entered upon here, to show that the earliest eruption, which 
was presumably that of the main gabbro mass, was before the 
Paradoxides epoch, and nia}^ have been the cause of the de- 
struction of the Olenellus fauna. 
Many other geologists have reached the conclusion that two 
series of crystalline rocks exist in the Adirondack area. Van- 
uxem, in 1842, distinctly states that in Lewis county he re- 
ferred certain metamorphic rocks to the Taconic system, 
(Report on the Second district, p. 135). T. B. Brooks, in 1873, 
called attention to sub-crj^stalline strata below the Potsdam 
sandstone in St. Lawrence county, which he suggested be- 
longed to the Taconic system (Am. Jour. Sci., (3), iv, p. 22, 
1872). The whole series observed by Brooks between the 
Potsdam and the gneiss was considered to aggregate 700 feet, 
but he did not find the bottom beds. A. R. Leeds in 1878 re- 
ferred the rocks of Essex county to the Norian system, which 
has been shown to be upper Laurentian (Thirteenth report of 
the New York state museum, pp. 79-109, 1878). C. E. Hall 
reached results similar. He attempted to express the strati- 
graphic order of the parts (Twenty-second report of the New 
York state museum, 1879, and the Fourth report of the State 
Geologist, 1884), viz.: (1) Limestones (verd-antique marbles, 
plumbago, etc.) and the Labrador series, or upper Laurentian, 
with its titanic ores, certainly non-conformable with the 
lower Laurentian and probably with the upper Laurentian. (2) 
Laurentian or sulphur ore series, essentially a series of quartz- 
ytes with dependent gneisses, associated with the labradorite 
rocks as a part of the upper Laurentian. (3) Lower Lauren- 
tian or magnetic iron ore series, Mr. Hall was not satisfied 
as to the stratigraphic position of the '^sulphur ores" and the 
associated quartzyte, but comparative studies of the iron ores 
of Minnesota seem to indicate that they are in a formation 
non-conformable over the lower Laurentian, though when 
crystallized the resultant gneisses and ores are easily con- 
founded with the older gneisses. 
Messrs. Pumpelly, Walcott, Van Hise and Geo. H. Williams 
in 1890 made a joint reconnoissance of the Adirondacks and 
while they do not precisely agree in all their results, the}^ are 
