312 Ornithichnology. 



seem to be any reason why they may not be traced farther, except 

 that the layer of rock containing them, is not laid bare beyond the 

 tenth track. It is also impossible to doubt that this, and all oth- 

 er continued tracks, were made by a biped. For we search in vain 

 to find any corresponding or parallel row of impressions. They 

 are not, indeed, exactly on a right line ; but the alternate tracks 

 deviate a little to the right, and the remaining ones to the left, 

 sometimes more and sometimes less, the toes being ordinarily turned 

 outwards. The interval, also, between the different steps, varies ; 

 sometimes several inches in the smaller impressions, and even a foot 

 or two in the layer : just about as much, indeed, as we should expect 

 in an animal moving at different paces. 



It has been interesting to observe, in almost every case where the 

 impression is distinct, how easy it is to determine whether it were 

 made by the right or the left foot of the animal. Even in an insu- 

 lated impression, this can be generally decided ; and where the 

 tracks are continuous, it is easy to see that the left and right foot al- 

 ternate. In the right foot, the toes, especially the middle one, are 

 slightly curved towards the left, so as to make the exterior side of 

 the bow on the right side of the track ; an effect resulting from the 

 effort of the animal to throw the body forward. The same effort 

 causes the outer part of the heel in the large tracks to appear as if 

 thrown behind the inner part, and the reverse of all this, is true of 

 the track made by the left foot. (See the plate appended, exhibit- 

 ing a proportional view of the tracks.) 



The inclination, or dip of the rock at the different quarries, va- 

 ries from 5° to 30°. Yet the animals seem to have passed over 

 it, while in a plastic state, in every direction with equal facility. At 

 the Horse Race, where the dip is 30°, they sometimes appear to have 

 ascended, and sometimes to have descended, and sometimes to have 

 passed diagonally ; yet the tracks are not at all changed by the steep- 

 ness of the declivity. There is no appearance as if the animal had 

 scrambled upwards, or slid downwards, except in one or two tracks 

 of great size, where the mud appears to have been rolled up a few 

 inches before the feet. But in this case, the animal was moving 

 horizontally, that is, along the line of bearing of the strata ; and even 

 on level ground, a heavy animal, moving at great speed, will pro- 

 duce this effect upon plastic matter. So that upon the whole, the 

 evidence is quite decisive, that these tracks were made before the 

 rock was elevated to its present situation ; that is, while it was hori- 



