W, E. Logan on an Animal Track. 17 
regular, distinet ape unmistakable strize such as would be, at once, 
- so recognized b eye practiced on the striz of other diatoms. 
Aas all, it is ee improbable, that true striz yet unresolved, 
may exist on the valves of this species, and sr ramen that the 
apparent strie of different observers may be similar to the spec- 
tral or spurious lines before noted as occurring on the bands of 
Nobert’s Test Plate, when examined by an aajoesive incapable 
of resolving them 
q summary of ‘the foregoing may be briefly stated thus :— 
that our experiments lead us to believe 
1st. That lines on Nobert’s Test Plate, closer together than 
about the ;,,1;; of an inch, cannot be separated by the modern 
se ye 
That no true strizs have yet been seen on the valves of 
ia hipleura pellucida. 
3d. That the alleged variableness in the striation of diatoms 
among individuals of the same species has been greatly exagge- 
rated: on the contrary, we find a remarkable uniformity, thus 
sustaining the opinion of Prof. Smith (Synop. Br. Diat., v. 2, 
Introd., p. 26) that for characterizing — “striation is the 
best guide.” 
Columbus, Ohio, Nov., 1860. 
Art. IIl.—0On the Track of an Animal lately foun in the Pots. — 
dam Formation; by Sir W. HE. Loean, F.R.S.* 
(Read before the Natural History Society of Montreal, June, 1860.) 
THE Potsdam sandstone is recognized in Danaea pre new 
York as the base of the Lower Silurian series 
are certain of the formation in the province it, rests agen Pel 
ably upon the Laurentian series; but on the north shore of Lake 
uron, the Huronian series supports unconformably a sandstone 
which has been supposed to be Potsdam ; as no fossils, howev Be 
ave been met with in it there, its equivalence i 
doubtful, ernie as the superior fossiliferous rock into hak 
it passes, appears to be of the Bird's. -eye and Black River group. 
arrande in a paper communicated to the Geological Soci- _ 
ety of France about a year ago, compares the Potsdam formation 
with the Primordial Zone, and Pea? Sanere to unite it with ~ 
the strata marked by Paradoxides n nin ichusetts 
and Placentia Bay in Nowiuntiasd” tt first locality 
Paradoxides Hariani which he identifies with his P. sp 
the latter Mr. Salter's P. Bennetii, and probably ot 
era and species. But while no well ascertal 
" # From the Canadian Naturalist, Aug. 1860. 
Am. Jour. srg et om au SS sa 
ste 
