396 C. H. Hitchcock on Impressions on Clay. 
those observed on this clay bed exactly resemble each other in 
orm and size. 
It may be added that we have found at this locality large sur- 
faces covered with scratches similar to the striae made upon stone 
by drift. e infer that the latter may sometimes have 
been made in a similar way. In the spring, the Connecticut river 
is swollen to an unusual size, and filled with masses of ice and 
floatwood. Driven by the current, they are forced over this bed 
while it is scarcely covered by the water. And thus the surface 
becomes covered with striz: all pointing in the same direction 
except a few which cross the others at a small angle. 
‘he phenomena of mud-veins are also illustrated by a fact 
noticed at this clay bed. Great heat causes clay to contract, 
as may be seen in deposits left by small pools of muddy water, 
which have been exposed to the sun. the surface of this bed 
in Hadley is similarly divided during seasons of drought. So 
when in Triassic times a clayey mud was cleft in this way, the 
returning tide, or a storm of rain would fill the fissures with de- 
tritus, producing the mud-veins which are very common in the 
rocks of the Connecticut valley. Another fact may be men- 
tioned here. The summers during which the best, specimens of 
these alluvial foot-marks were obtained, “vere quite ty, Ifalong 
rought succeeded a copious shower, a pe crop of tracks was 
gathered. Hence it may be inferred, that &hen the Triassic ich- 
nolites were made, the climate was tropical. This will explain 
the remarkably fine preservation of delicate ichnolites. ~ 
This locality serves to explain why among so many fossil foot- 
marks as have been disinterred, scarcely a relic of the animals 
themselves have been found. For three years I have not notice 
on coi clay bed any other trace of the animals besides their 
tracks. 
