276 L. Agassiz on the Primitive Diversity 
inerease of the species found in the different paleozoic de- 
posits show that, even in point of numbers those ancient 
faunze may, even in the present state of our knowledge, be 
compared with local faune of similar extent at the present 
day. 
Desirous of making the most accurate comparison possible 
between the subdivisions of the paleozoic formations of the 
“state of New York with local faune of similar extent in the 
present seas, I have requested Professor J. Hall to furnish 
me with summary indications respecting the results of his 
extensive investigations in this field, and I have obtained 
from him the following statement :— 
“JT regard the Potsdam and Calciferous Sandstone as 
disconnected with the groups above, forming of themselves 
with their fauna (not yet well known in this country) a dis- 
tinct geological period. The entire number of species thus 
far known in these rocks, admitting all of Owen’s species, is 
however only twenty-six. 
‘The Chazy Limestone has 45 species restricted to itself, 
and one other species which is also known in the Black 
River Limestone. The Birdseye Limestone has 19 species 
restricted to itself, and two others which pass upwards. The 
Black River Limestone has 13 species restricted to itself, 
and one common to it and the Chazy limestone, one common 
to it and Birdseye, and one common to it and the Trenton, and 
one other which is common to the beds below and above, ex- 
tending into the Hudson River group,” making together 81 
species for these three sets of beds. 
“The Trenton Limestone has 188 species restricted to it- 
self, and 30 species passing upwards into the Hudson River 
group. The entire number of species known as occurring in 
the Trenton Limestone, including those which occur in 
rocks above and below, is about 230. This statement in- 
cludes some species discovered since the publication of the 
1st volume of the Paleontology of New York, and which 
would make the restricted species about 200. 
“The Hudson River Group, including Utica slate, has 
about 60 restricted species, besides those which are common 
to it and the rocks below, making altogether about 100 , 
species. 
-—. . 
