18 W. E. Logan on an Animal Track 
cies have been met with in the Potsdam of Canada and New 
York, the formation appears in Canada to be rather allied to the — 
strata above than those below it. 
dam is characterised in many parts. 
Immediately beneath these beds of passage are the celebrated 
| : assion 
which is about an eighth of an inch below, shews wind-mark, in 
a number of sharp and straight parallel ridges from two to four 
n being marine, we have 
Proverbially unstable as water is, the niean. evel of us ee 
between high and low water, 
* Since this paper was read two ies of Orthoceras Ophileta ‘deta have 
adaeieed ex Canada associated with Lingula posh we Real ers Sand- 
stone. The trilobite Conocephalites minutus (Bradley) has also been since described. 
