1885.] in Pennsylvania and New York. 649 - 
distinguish certain horizons, as Professor Hall describes them, 
but without sharp and decisive limitation to these horizons. 
It is farther possible, and not improbable, that these zones of 
maximum abundance hold the same relative positions to one an- 
other in New York and in Pennsylvania. This, however, must 
be decided by closer study. Nothing that the writer has seen or 
published is antagonistic to such belief. But even if the zones of 
maximum abundance should not hold the same relative positions 
to one another in different parts of the country, we are not driven 
to the alternative of asserting a “subversion of specific types in 
vertical range ” (p. xxvi). Given the three species, or indeed any 
two of them, living side by side through the greater part of the 
Chemung era, and we need only admit that local conditions favored 
here the one and there the other, and the whole difficulty disap- 
pears. It is purely imaginary. It is scarcely probable that iden- 
tical conditions of life existed contemporaneously over so great 
an area, it need not consequently shake our belief in palzontol- 
ogy if the result should show that in Pennsylvania and Virginia, 
or in States still more distant, the zones of maximum abundance 
hold an order different from that which Professor Hall has laid 
down for New York. 
Another fact may be mentioned in this connection which, 
though not directly connected with the argument, yet serves to 
show that the lines of delimitation bounding the range of fossil spe- 
cies cannot be laid down as definitely as has been done by some 
palzontologists. - S. /evis is one of the characteristic fossils of the 
Portage group in New York State occurring neither above nor 
below, so far as the writer is aware. Yet in Middle Pennsylvania 
it has not been found in the strata occupying the position of the 
. Portage of New York, and holding other Portage fossils. But it 
does occur higher up, in the Chemung proper, and in company 
with S. mesocostalis S. levis, it may be added, is a well charac- 
terized species in New York, and is therefore readily recognized. 
HL 
Passing on to another topic, we find on page xxii: 
=“ Orthis tulliensis has certainly never been seen before in the 
Chemung two hundred feet above the Genessee (ż. e., three hun-, 
dred feet above the Tully limestone), nor in the company of S. 
mesocostalts,” 
1 This is possibly S. mesostrialis. The specimen is only a fragment. 
