254 The Aiiienaiii Geologiat. octobf r, i89r 
in their ihiiracters; outside of these centres the species exhibit varieties 
which may be called oxtra-limital, aud which are not typical though 
they liave often been published as types. 
Dr. F. Freeh said that in comparing the middle paleozoic fauna of 
Europe with that of North America, there were two principal points of 
especial interest: 
A. The identity of some comparatively small horizons. 
B. The far greater differences that exist in these same beds. 
The similar faunas are — 
1. That of the Niagara and of the Wenlock shales. 
'..*. In the Upper Devonian the Rhynchonella of the Tully limestones 
and the Goniatites of the so-called Naj)les beds. 
3. The Goniatites at the base of the Carboniferous in Iowa, in Spain, 
and in middle (Germany. 
The Hamilton fossils are of especial interest because we have on the 
Rhine, in the so-called Lennenschiefer, a fauna of the same fades. 
But while these rocks were deposited under similar physical conditions, 
the number of identical species in the two countries is very small, and 
there are many senera in each country not found in the other. All the 
Lower Devonian is wanting in European Russia and part of it is want- 
ing in middle Germanv, but the great physical change which followed 
is sufficient explanation for the differences which characterize the junc- 
tion of the Devonian and Silurian. 
Prof. Barrois thinks it impossible to compare in detail American and 
European rocks. Soma individual zones of the American series can be 
correlated with European horizons, but it is quite impossible to estab- 
lish in detail the ideotit}'^ of other and adjacent zones. 
Prof. C. R. Van Hise spoke of the distribution, character, and succes- 
sion of the pre-Canibrian sedimentary rocks of North America. All 
rocks are regarded as pre- Cambrian which are earlier than the Olenellus 
fauna. These rocks contain the evidence of abundant life as shown by 
thick beds of carbonaceous shales, by various distinct fossils, and in 
many other ways. When a less highly developed fauna is found, as 
different from the Caml)rian fauna as the Cambrian is from the Silurian, 
it is best to give this fauna a new name. 
There are in many areas in North America great thicknesses of little 
altered pre-Cambrian sedimentary rocks. In many regions these rocks 
have been separated into series by wide-spread unconformities, and 
these series have been farther divided into formations. Some of the 
more important pre-Canibrian regions are Lake Superior and Lake 
Huron, Central Arizona, New Brunswick, Newfoundland, Southwestern 
Montana. As an illustrative example of the successions may be cited 
the first. In this area the descending order is Lake Superior sandstone 
( Potsdam), unconformity, Keweenawan,unconformit3-, upper Huronian,^ 
unconformity. Lower Huronian, unconformity, basement crystalline com- 
plex. Each of these series is divided into several formations. 
In individual regions it is possil)le to correllate series and formations 
upon a jihysical basis. In different regions the series have variable 
