The Tdconic or Lower Cambrian. — WincheU. 301 
in accord on the point on which we wish to insist at this place, 
viz., there is in this region a very important series of modified 
elastics which are not of Laurentian age, and lie unconforma- 
ble below the Potsdam sandstone. This series consists of 
quartzose gneisses, crystalline limestone, grai)hitic gneisses, 
and magnetic iron ore. Van Hise says:* 
"While tho interior structure of the rocks of tliis series now shows no 
positive clastic characters, the limestones, graphitic schists, and regu- 
larity of what appears to be bedding in the gneisses leave but little 
doubt that the series was originally clastic and belongs lo the Algon- 
kian. The studies of Walcott render it probable that there is here also 
a basal complex, and along the contact lines of the series Walcott has 
discovered evidence of an unconformity. This Algonkian is so remark- 
ably like the not far distant original ui)per Laurentian, in the neighbor- 
hood of Ottawa, that one cannot doubt that the two are, or once were, 
continuous." 
In 1892 the writer, accompanied by Dr. U. S. Grant and INFr. 
Charles Schuchert, made a reconnoissance of the northern 
portion of the Adirondacks.f We found a gneiss interstrati- 
fied with marble and quartzyte, some of the gneiss also being 
very quartzose, the contained free quartz being estimated, in 
thin section, at 50 per cent., the rest being mainly some feld- 
spar. These were considered to be essentially of the same 
age, but post-Laurentian, although the existence of the lower, 
older gneiss was not ascertained. Not only were there frag- 
ments of gneiss embraced in the limestone, but isolated lenses 
of limestone were found embraced in the gneiss. This upper 
series of gneiss, quartzyte and limestone was parallelized, in 
the report, with the Taconic series of western New England, 
not only because of evident lithological differences from the 
true Laurentian of the northwest, but because of a similarity 
in order of parts and of general character with the Taconic 
series on the eastern side of the Adirondacks. We did not, 
however, ascertain whether the rocks qunrfzyte, limestone, 
(/neis.s, which were found succeeding each other, increased in 
age from quartz3'te to gneiss, or vice versa. 
In 189B Mr. F. L. Nason correlated the magnetic iron ores 
of the Adirondacks and their associated rocks with the iron 
*U. S. Geol. Sur., Hull. No. 86, pp. 398, 508, 1892. 
fTwentv-first annual report of the Geol. and Nat. Hist. Sur. of Min- 
nesota, pp. 99-112, 189:5. 
