1s 
deepest, the toes are very strongly indicated. On the 
same surface are impressions of nails, which may have 
belonged to birds or chelonians. 
The inferior surface of the same slab exhibits 
appearances more superficial, less numerous, but 
generally regular. There are three sets of tracks 
entirely distinct from each other; two of them con- 
taining three tracks, and one containing two, — the 
latter being much the largest in size. In addition, 
there is one set of tracks, which are probably those of 
a tortoise. These marks present two other points 
quite observable and interesting. One is that they are 
displayed in relief, while those on the upper surface 
are in depression. The relief in this lower surface 
would be the cast of a cavity in the layer below; 
so the depressions in the upper surface would be 
moulds of casts above. ‘The second point is the non- 
correspondence of the upper and lower surfaces; i.e. 
the depressions in the upper surface have not a general 
correspondence with the elevations on its inferior sur- 
face. ‘The tracks above were made by different indi- 
viduals and different species from those below. ‘This 
leads to another interesting consideration, that in the 
thickness of this slab there must be a number of 
different layers, and in each of them there may be 
a different series of tracks. 
