AT STOURTON HILL. 47 



alone ; — but all agreeing with the impressions of the reeds 

 and branches of trees, in indicating a great river or estuary 

 opening remotely into the sea, and that the Chirotherium it- 

 self may have been also semi-aquatic, like the crocodiles and 

 Emydes of existing shores. 



In the crocodilian reptiles, of which numerous gigantic re- 

 mains abound in the lias deposits, nearly as ancient as this 

 rock ; the hands are proportionately very short and broad, 

 and pentadactylous, as in this Chirotherium, and the outer 

 finger projects, short and free, as the supposed inner finger 

 or thumb in the animal before you. In these reptiles, also, 

 it is the outer, and not the inner toe, of the proportionately 

 large hind feet, which is short and rudimentary ; and there 

 may have been great diversities in the extent or freedom of 

 this outer rudimentary hind toe in the various Teleosauri, 

 Steneosauri, and other semi-aquatic forms of reptiles which 

 have long become extinct like the Ichthyosauri and Plesio- 

 sauri which swarmed at the same period in the ocean. If 

 we suppose the free projecting toes of the Chirotherium to 

 have been inner toes or prehensile thumbs, this animal must 

 have crossed the line of gravity of its body with its feet, at 

 every pace, in bringing them to the ground, as may easily be 

 perceived by carrying the eye along the line of footmarks. — 

 Although this supposition agrees with the developement, if 

 muscular and not osseous, at the base of the thumb, it forces 

 us to believe that this animal crossed the right foot to the 

 left side of the line of gravity of the body, by the entire 

 breadth of that foot, before it reposed it upon the ground, and 

 that the left foot, to the same extent, crossed over to the right 

 side before it rested to support the trunk. But, if the sup- 

 posed thumbs, which here curve backwards in a manner ex- 

 traordinary for such members, be only forms of the short out- 

 er toes of the large hind feet of crocodiles, gavials, and alli- 

 gators, the feet no longer cross the median line of the body, 

 but assume the positions seen in the walking of most other 

 reptiles. Although I have not been able *to find any shells, 

 bones, or other organic relics in these rocks, nor have heard 

 of any having been observed by others, the ordinary ripples 

 seen on the sands of the seashore, and on the banks of lakes, 

 are every where common and distinct in the sandstone of this 

 quarry. In the upper stratum of the footmarks there is a re- 

 markable pitted appearance over the surface of the impressed 

 clay, as if produced by drops of rain, or by the unequal shrink- 

 ing of the clay in drying, and this often produces a warty ap- 

 pearance in the casts of the footmarks. In some of the spe- 

 cimens preserved I perceive smooth, rounded, broad markings, 



