IMPRINTS ON SANDSTONE. 327 



would requii-e a volume expressly devoted to the 

 subject. A few additional remarks are, however, 

 necessary on some anomalous appearances in the 

 sandstone of Brixton Bay, that have recently 

 come under my notice. The occurrence of im- 

 prints resembling the foot-tracks of birds and 

 reptiles, on the surface of slabs of sandstone of 

 very ancient formations, must be known to the 

 well-informed reader, from the lucid illustration 

 of the subject, in Dr. Buckland's Bridgewater 

 Essay. Among those supposed foot-prints are 

 several of large dimensions, described under the 

 name of Chirotherium, which are conjectured to 

 have been made by some enormous three-toed 

 reptile, passing over the stone when it was in a 

 soft state. Others equally colossal, from the 

 arrangement of the markings on the slabs indica- 

 ting the progressive footsteps of bipeds, have been 

 ascribed to gigantic extinct birds.* The layer of 

 clay, or sandstone, overlying these imprints, gene- 

 rally retains casts of them, which appear in relief 

 on the surface of the slabs when removed ; in 

 other instances the cast of a single mould alone 

 remains, and being more consolidated than 

 the matrix, is often extracted whole. Several 

 large sandstone casts of this kind were dis- 



* Medals of Creation, p. 708. 



