362 R. Field on Fossil Foot-marks. 
not always found on the surface where the foot rested, the weight 
of the animal causing the foot to sink through ae ‘stra 
is we kn0 
was the case with animals that were surely quadrupeds, but 
for we should naturally suppose that where so large @ num ail 
birds congregated upon the muddy banks, that in dressing 
all of them. The smoothness of the bottom of 
fossil tracks agrees better with some species of batracne 
now live in and about the water, than it does with . 
as live on the land. Had birds existed at this ea" e— 
ical : 
being deposited, there has indeed been a woful Fite . 
tory, from then up to near the historical period, . 
