208 Dr DUNCAN on the Footmarks of Quadrupeds 



any impressions which animals might have made at low water, 

 by moving over the surface of the sands they were depositing. 



In the midst of so much difficulty, it is not easy to form 

 even a plausible conjecture as to the manner in which the sand 

 composing the rock was originally accumulated. It might, 

 however, be perhaps worth while to inquire whether or not this 

 successive accumulation could be the effect of the drifting occa- 

 sioned by violent winds from the south-west. Supposing a sand- 

 hill to be thus formed, a period of rainy weather following the 

 stormy season would soften and diffuse the particles of clay, 

 which may easily be believed to have mingled with the sand- 

 drift, and would not only prevent the sand from being again 

 moved by the wind, but would form it into a substance of some 

 tenacity, resembling mortar, well fitted for preserving any im- 

 pression it might receive. If, during or immediately after the 

 rainy season, animals were to traverse a hill thus formed, their 

 tracks would be either altogether obliterated, or partially filled 

 up, of which latter state many traces are to be found in the 

 quarry ; but when the surface had begun to dry, the foot-marks 

 impressed on it would remain for a considerable time quite dis- 

 tinct and well defined. Now, supposing the stormy monsoon 

 again to commence, the neighbouring sands, which had not yet 

 been fixed by any strong mixture of clay, and which happened, 

 from their situation, to be easily dried by a few days of favourable 

 weather, would be suddenly drifted on the hill in question, form- 

 ing a layer which may easily have covered over the half-indurated 

 surface, without being incorporated with it, and without in any 

 way injuring the form of the foot-steps imprinted on it. Let the 

 monsoon be now supposed to continue during the whole course of 

 a dry summer : Fresh layers of sand would be drifted, compara- 

 tively pure at first, but mingled again towards the close of the 

 season with the clayey dust swept from an arid soil, which mix- 

 ture would form the materials of what the quarrymen know in 



