Dr. Deane’s Letter to Dr. Mantell. — » I8t 
tained by the divergence of the toes, the progression and alter- 
nation of the feet, and the existence in each variety of steps 
of an identity or individuality as unequivocal as is ever displayed 
in animated nature. The examples xv, xvi, xvi, xvii, are in 
point. If you will place them in the order of numbering two 
and a half feet asunder, which was the length of the stride, so 
that the connecting line shall fall a little inside of the centre of 
each impression, they will occupy their original positions, and it 
will be observed that the long toe is alternately upon either side 
_ of this line. Indeed we may sometimes follow the route of the 
bird several rods, step after step, and the sight is sufficient to fill 
the beholder with astonishment; he is irresistibly carried backward 
through the long series.of years, until lost in the unsatisfactory 
computation of the era in which these impressions were made. 
Their existence upon the face of the rock, without any excep- 
tion, is in strict conformity to the laws of nature. The footsteps, 
invariably those of a biped, occur upon the upper surface of the 
stratum, while the cast or counter-impression is upon the lower. 
Not a single deviation has ever occurred. ‘The reverse impres- 
sion is beautifully illustrated: by the specimen No. xu. It is 
moulded by a subsequent deposition in the matrix, formed by 
the foot of the bird, and it is an indispensable condition, which 
universally exists. The foot is usually tridactylous, although 
there is the same deviation from. this condition, as is found in 
living birds. There are usually three, sometimes four, but rarely 
five toes. The length of step is in correspondence with the di- 
mensions of the foot. °When it is one inch in length, the inter- 
vening distance of the step is from three to five inches, but when 
the foot-is fourteen inches and upward, the stride is from four to 
six feet! When I talk of a foot fourteen inches in length, it may 
appear incredible that the earth ever produced such a colossal 
‘ird, but~if you refer particularly to No. xxx, you will find it of 
full meastire, and that:without a projecting heel! I am particular 
to state, that its el us magnitude consists entirely of the three 
toes, the heel not to th ind. It is altogether a remark- 
able impression by reason of its size, and perfect delineation. 
With the exception of the lateral claws, it is accurate as any spe- 
cimen I have ever seen, and as it is a shallow impression, it is best 
seen by placing it at a distance of ten or twelve feet, in the re- 
flection of a strong light. In all these remains the distinctive 
