a2 
four legs, gives us the impressions of two only, and 
both of these placed together. 
When the tridactylous tracks are attentively con- 
sidered, compared with each other, and with the 
digitated tracks, they appear to exhibit the character 
of the impressions of the feet of birds so very 
decidedly, that it would require something more than 
a philosophic incredulity to question their ornithic 
origin. 
The other side of this slab contains interesting 
impressions. In the first place, this surface is covered 
with ripple-marks, each about two inches broad, 
extending with various degrees of distinctness across 
the slab, and having an interval of an inch. The 
width of the ridges is greater than in any of the 
specimens we have seen. 
This surface is almost covered by rain-drops. It 
has also, among other impressions, one which has 
been drawn by Mr. Silsbee, our photographist, and 
represented by the figure below of its proper size. 
This figure, nearly four and a half inches in length, 
is an exact resemblance in form, but not in size, of 
the great Otozoum, as depicted by President Hitch- 
cock, and shown by the actual impression, in our 
hands, of the great foot, twenty inches long, and of 
proportionate breadth. The form of the heel, or pos- 
