THE GEOLOGICAL MIDDLE AGE. 151 
which, except for these footprints, remain un- 
known to us. In the sandstone of the Connecti- 
cut Valley they are found in extraordinary num- 
bers, as if these animals, whatever they were, 
had been in the habit of frequenting that shore. 
They appear to have been very diversified ; for 
some of the tracks are very large, others quite 
small, while some would seem, from the way in 
which the footsteps follow each other, to have 
been quadrupedal, and others bipedal. We can 
even measure the length of their strides, follow- 
ing the impressions which, from their succession 
in a continuous line, mark the walk of a single 
animal.* The fact that we find these footprints 
without any bones or other remains to indicate 
the animals by which they were made is ac- 
counted for by the mode of deposition of the 
sandstone. It is very unfavorable for the preser- 
vation of bones ; but, being composed of minute 
sand mixed with mud, it affords an admirable 
substance for the reception of these impressions, 
which have been thus cast in a mould, as it were, 
and preserved through ages. 
These animals must have been large, when 
full-grown, for we find strides measuring six feet 
between, evidently belonging to the same animal. 
In the quadrupedal tracks, the front seem to have 
* For all details respecting these tracks see Hitchcock’s Ich- 
nologi/ of New England. Boston, 1858. 4to. 
