252 Robert Harkneas, Esq., on Fossil Footprints. 



The absence of the impress of the fore-feet in beds which 

 have originally been saturated with water, appears to arise 

 from the circumstance that these animals in their progres- 

 sion caused their hinder extremities to form a deeper im- 

 press than the fore ones ; and. this affords another proof of 

 the universality of the laws of nature, not only so far as 

 present existing races are concerned, but likewise during 

 periods long antecedent to the present order of things ; for 

 it is a fact that all walking animals have their posterior 

 extremities so organised that in them shall reside to the 

 greatest extent the power of progressive motion. The im- 

 pressions are usually found in the most beautiful state of 

 preservation ^vhen they occur either on the surface of a bed 

 which contains a small portion of clay in its composition, or 

 on a thin deposit of clay itself. When either of these is the 

 case, the impress of each pair of feet is distinctly seen, shew- 

 ing the form and arrangement of the toes or claws, and the 

 hinder pair of steps are generally more perfect than the fore 

 ones, which have often become partially obliterated by the 

 hind feet treading upon the impressions caused by the fore 

 ones. The reason why the footprints in this substance are 

 in so perfect a state, is owing to the clay preventing the sand 

 from falling into the impressions, and the nature of the ma- 

 trix receiving the steps is such as to afford a soil sufficiently 

 soft and yielding to receive a perfect impress, and, at the 

 same time, sufficiently tenacious to retain all the fine traces 

 left by the step after the foot had been withdrawn from the 

 impression. The circumstances attendant on the occurrence 

 of footprints when they are met with in this matrix, are such 

 as appear most favourable to the perfection of impressions. 



The different states of preservation in which the impres- 

 sions occur, furnish us with important information concern- 

 ing the nature and condition of the surface over which the 

 reptiles passed. In the imperfect traces which are found, 

 not only on the surfaces of some of the strata, but also in 

 the interior of the stone when this is split along the laminae 

 of its bedding, we have evidence of a soft sand not cohesive 

 enough to retain distinct forms of footprints. In those im- 

 pressions which have a rounded outline, we see a surface 

 which at one time was yielding and tremulous, representing 



