C. H. Hitchcock on Impressions on Clay. 393 
perfect tracks of this species in rows several yards long, and 
ave been found in relief, by splitting open the layers 
of clay. A few thousand years might so petrify the impressions 
and their casts, that they could not be distinguished from fossil 
foot-marks, except so far as difference in species is concerned. 
The tracks of two other species of birds, one of them, perhaps a 
_Tringa, have been found; but with no additional character of 
importance. 
Of the two genera of quadrupedal tracks noticed, those of the 
dog only are recognised. In some specimens, because of the 
toughness of the clay, the claws merely are impressed. A care- 
ess observer might suppose that these canine impressions were 
made by a biped, because he sees only an apparently right and 
left foot-mark. Buta close examination shows that every track 
is double: that is, the hind-foot steps into the tracks of each fore- 
foot. In other cases, instead of being double, the two tracks are 
placed side by side very near to each other. The marks of hair 
may be seen on some specimens. ‘The papille of the dog and 
crow are quite similar. 
| _ At another place there were impressions in two long rows 
which were possibly produced by a young bird—the progress of 
Tringa minuta, perhaps. Others were made by a frog at rest. 
; Of these last, the two largest were made by the hind feet; they 
are toed in. An oval spot between the tracks was probably 
made by the body of the animal. 
Another class of impressions forms irregularly curved lines. 
ese may have been made by the smaller Conchifers and Mol- 
/ lusks, Unio and Paludina: of course, different species which were 
of the same size could not be distinguished from each other by 
their tracks. 2 fioepiee 
!The trackway of an Annelid is very distinct. It is a continu- 
ous fimbriated trail, depressed in the centre throughout its whole 
extent and elevated along its edges. At least two species have 
g 
__ The surface of the denuded clay is somewhat uneven. Every 
ume it rains the depressions become filled with water, thus 
Making small pools of muddy fluid, which form a deposit admi- 
tably fitted for receiving impressions. Upon this soft stratum, after 
the water has nearly dried up, animals tread, leaving the imprints 
Of their feet. Subsequently the deposit b dened by the 
-—— Sreoxp Senses, Vol. XIX, No. 57.—May, 1855. 50 
