652 On the Vertical Range of Certain Fossil Species [July, 
Immediately above the limestone bed in question comes the 
Oriskany sandstone, so that the evidence for position is rendered 
doubly sure, and it would be idle, in the face of all the facts, to 
entertain any remaining doubt or suspicion regarding the horizon 
or the species of the fossil. It is Halysites catenulatus, and it is 
found in the Lower Helderberg limestone. 
Halysites catenulatus ranges in England from the Llandeilo up 
to the Wenlock, and in America from the Trenton to the Niagara, 
by consent of all geologists. At this horizon its disappearance 
has been assumed. But the determination here maintained car- 
ries it up through about 1200 feet of strata, and extends its spe- 
cific life through a correlative lapse of time. 
In the consideration of these facts it may be remarked that the 
very ease and certainty with which this fossil can be recognized 
appear to the writer a possible source of error. Being abundant 
at numerous places in the Niagara limestone, it forms a convenient 
fossil reference, and its range has been, by tacit consent and per- 
haps with the aid of influential names, assumed to be limited 
upward by the summit of the Niagara. It has thence become the 
practice to refer ail strata containing it to the Niagara group, and 
the two have become closely associated. Yet the foundation for 
so strict a delimitation is as unsatisfactory as in the cases pre- 
viously examined. It is in fact another instance of vicious rea- 
soning. Halysites catenulatus occurs very frequently in Niagara 
rocks, therefore all rocks yielding Halysites catenulatus are of 
Niagara age. : 
If this fallacy be avoided and the. upward range of Halysites 
be admitted, its occurrence in the place and on the horizon men- 
tioned by Professor White (in G,) instead of being “ a serious 
matter for Pennsylvanian geology” (p. xxiii), may be a matter of 
importance to the geology of some States outside of Pennsylva- 
Nia, and may even cause the removal to a higher level of some 
strata which have been hitherto placed in the Niagara group by 
the hasty deduction above condemned. 
For example, it is just possible, to say no more, that the occur- 
rence of this fossil in the cement beds, as at Kingston, N. Y., 
may be hereby explained. If these cement beds are the same as 
. those usually included under that name, they should lie in the 
: Lower Helderberg series and not in the Niagara, as often stated. 
Moreover a reference to Professor Hall’s geological map of New 
