Miller on the Taconic. 243 
and bearing no more than a mere trace of phosphorus. The 
rocks appear in numerous places in the Rocky mountain ranges 
from Mexico to British Columbia, often exposing great geo- 
graphical areas and an immense thickness, and usually metallif- 
erous. 
The genera regarded as typical of the Taconic fauna and 
which do not pass up into Silurian rocks, are Paradoxides^ 
Mtcrodiscus^ Atops^ or Ptychofaria^ Olenellus^ Conocoryphe^ 
Anopolemts^ Bathynotus^ Solenopleura, Acrothele^ Salterella^ 
Scenella^ Iphidea^ Hyolithellus^ Arckceocyathus and Bth?no- 
phyllum. There are some others peculiar to these rocks, but 
they are either obscure or limited in their distribution. Some 
genera closed their existence in Silurian time, others reached 
the Devonian age, and some, from this remote period, as Orthis^ 
Orthisina^ Ot'thoceras^ and Leperdiiia, continued to live to the 
Carboniferous, through Orthoceras reached its most remarkable 
development, in the Black River group, and Orthis^ in the 
Hudson River. Not a single species belonging to the Upper 
Taconic system crossed over the line that separates it from the 
Potsdam group of the Lower Silurian so far as any reliable 
determination has thus far been made. This, supported as it is 
by a want of conformability, indicates a vast lapse of time be- 
tween the deposit of the Upper Taconic and the commence- 
ment of the Potsdam period. The Taconic is composed of the 
disintegrated materials of prior Laurentian rocks, while the 
Potsdam represents the washings of the Laurentian and Ta- 
conic. 
The Cupriferous series of the Lake region, called also the 
Keweenawan, Keweenian, Keweenawian and Nipigon series, is 
supposed to underlie nearly the whole basin of lake Superior, 
or an area of about 28000 square miles, and a surface area, upon 
the borders of the lakes and their immediate vicinity, of about 
18000 square miles. This series has been divided into an upper 
and lower division, with an estimated maximum thickness of 
15000 feet for the upper division, and 35000 feet for the lower 
which rests upon the slates andquartzytes of the Taconic system, 
the last having a variable thickness that reaches a maximum 
of at least 22000 feet. The Cupriferous series consists of erup- 
tive flows and detrital rocks, with massive dikes. The region 
