Robert Harkness, Esq., on Fosail Footprints. 251 



Whether their great abundance here be owing to this de- 

 posit being of a nature more capable of receiving and retain- 

 ing impressions, or to reptilian life prevailing to a greater 

 extent during this period, or to the sandy nature of this 

 deposit forming a suitable habitat, is a question which yet 

 remains to be answered. In this formation, however, many 

 and various forms of reptiles have left their tracks, and these 

 tracks are in a much better state of preservation than those 

 which the other formations afford. 



Variegated sandstone, from whence the great bulk of the 

 ichnolite markings are obtained, generally affords them in 

 two conditions ; one in which they are seen on the upper 

 surface of the sandstone strata, and consisting of depressed 

 markings, and the other when they occur in the under side 

 of the stony layers, in which case the footprints are in re- 

 lief, and form natural casts of impressions, commonly from 

 a clayey deposit, which is usually too thin to be removed 

 perfect from its original bed. The character of these im- 

 pressions, so far as their perfection is concerned, depends in 

 great measure upon the nature of the substance receiving the 

 footstep, as well as upon the action of the water transport- 

 ing the sandy matter which covers up and overlies the strata 

 containing the impressions. When the animal has traversed 

 a dry, sandy shore, we have the footprints distinct, so far as 

 order and succession go, but, owing to the yielding sand 

 trickling into the impressions as soon as the foot which 

 caused them had been withdrawn, these tracks rarely pre- 

 sent that sharp and definite outline which would enable a 

 satisfactory conclusion to be drawn from them, concerning 

 the form and nature of the animal to which they owe their 

 origin. If the nature of the substance over which the ani- 

 mal walked was originally in a state approaching to quick- 

 sand, from its being saturated with water, then the character 

 of the impression has been greatly modified. Under these 

 circumstances, it usually happens that the marks of the fore- 

 feet have been obliterated, while the hinder ones consist of 

 a series of steps, with a rounded outline in front, and gra- 

 dually becoming shallower behind, until they are each about 

 the level of the face of the stratum receiving the impression, 

 and the back-j)art of the footprint is commonly lost sight of. 



