394 C. H. Hitchcock on Impressions on Clay. . 
heat of the sun, and the tracks of course remain upon the clay as 
distinct as when first formed. Another storm arises, and a new 
stratum is brought on, covering up the former Jayer, without ob- 
literating the tracks. When the water has retired, this second 
deposit is trod upon, and hardened in the same manner as the 
first. At the same time the new layer fills up the recently made 
tracks. Thus an exact cast of the forms of the tracks is pro- 
duced. A third stratum protects the impressions upon the second 
deposit, and in this way the process may go on indefinitely. 
Having dug up and cleared the successive layers, the tracks in 
relief, as well as the corresponding depressed ones, have been 
found, as was sci in the description of the foot-marks made 
by the 7" Tringa m 
Now let us Sanaiiet the condition in Triassic times, when the 
Connecticut valley was an estuary. Upon its shore after a plen- 
tiful rain, birds and other animals were seattered along in search 
of accustomed food. ‘The heat of a tropical sun quickly hardens 
the first stratum impressed with tracks. Another shower comes, 
or more probably the tide rises, and a second Jayer is brought on, 
covering up the impressions just formed. This too in turn re- 
eives the impress of feet and becomes hardened, as may also 
others in succession till the sandstone of the whole valley above 
the tracks, at least a mile thick, was deposited. And since ani- 
mals seek their food chiefly along the margin of the water, we 
ek rock, usually over only a few feet in width, impr 
with tracks. 
The correspondence between the habe and Triassic impres- 
sions extends to every minute point. both formations appears 
the same alternate order of right and lef foot. They are found 
in relief in each instance. The phalangeal impresssons are anal- 
ogous in both periods. The print of the claws, also, is quite 
distinct upon stone as wel 
Tetrapodal ichnolites find allavial counterparts at this locality. 
The form of feet and manner of gait of the Dog and Anisopus 
Deweyanus somewhat resemble each other. The fore-feet how- 
ever, in the fossil species, are much smaller than the hind. But 
the impressions, instead of being situated at an equal distance 
from each other, are arranged by twos—a large and a small track 
together. This peculiar arrangement arises from the structure 
of quadrupeds, and the rapidity with which the animal moves. 
The swifter the movement the —_ nearly the hind foot is 
brought into the place of the fore o : 
The tracks of a frog correspond wel with the ichnolites of 
t s scambus. There are specimens of the impres- 
sions of this animal in the cabinet of Amherst College, sees 
‘it to bea a huge batrac sheet men sien and like the spe- 
eimen on clay. The impressions of the ifers and : 
