146 Hoio is the Camhrian divided ? — Matt/ie'M. 
dia) LeptoplastuH occurs. In the latter area also the fourth 
Cambrian fauna has been found, being indicated by the pres- 
ence of Ctenopyge Hagillifor, C. spectahilis and Orthis lenti- 
cularis. 
A fuller presentation of Upper Cambrian forms is that 
which is found in the Mississippi valley in the states of Wis- 
consin and Iowa, where there is a succession of 600 feet 
of sandstones whose fauna has been described and figured by 
Prof. Jas. Hall. He divides this series into three parts, the 
lowest of which contains forms similar to those at the base of 
the Olenus zone in Europe. 
In the middle division which is most prolific of the 
remains of trilobites, are species which may be compared to 
those of the genera Olenus^ Paraholina, Leptoplastus, 
Euloma and Conocephalites. Dr. Dames compares others to 
Anomocare. It is only in the highest Potsdam division and 
in the beds above it according to Prof. Hall that the typical 
Dicollocephali appear, and these in Europe are found in the 
Tremadoc or fifth Cambrian fanua. Triarthrella occurring 
in Wisconsin with these Dicellocephali is compared by 
Brogger to Cj/clognothus, a genus of the fourth fauna and of the 
base of the Ordovician. The whole series of 600 feet in Wis- 
consin seems to belong to the Upper Cambrian. But the 
phase of the fourth Cambrian fauna represented in Europe and 
Acadia by Ctenopyge and its allies is absent, probably from 
the want of favorable habitat. 
Comparative hulk of measures holding the faunas. 
The relative age and position of the Parad oxides beds inthe 
Cambrian system may be shown by the bulk of the measures 
in the different parts of the system. With our present knowl- 
edge this can be only imperfectly done, but the following is a 
comparison of the mass of deposits in three different coun- 
tries. When the system has been more carefully studied in 
different ])arts of the world a more exact proportion in the 
sedimentation will be had. 
In Norway the Cambrian system has the following thick- 
ness.* Ratio. 
Stage .3rt==Trema(loc or Ceratopyge fauna 45 feet. ... 1.2 
"' 2d-c=DolgelIy or Peltura fauna 40 " .... 1.0- 
" 2a-c=Lower Lingula flags, Olfnus fauna 110 '"' ... 3.2 
* Die ;-Mlur.sclien Etagen 2 und 3. 
