185 



by the elastic undulation of the fluid moulding the movable sedi- 

 ments into wave-like grooves and ridges, having the semblance 

 of the ripple transmitted to the bottom of shallow waters by the 

 wind, he showed how easily this appearance in the strata may 

 lead geologists to erroneous inferences as to prolonged subsi- 

 dences of the earth's crust where the phenomenon abounds. 

 The footprints of birds and reptiles on the rocks, give evidence 

 which is less fallacious, for they indicate, without any ambiguity, 

 that they were impressed in marine or tidal strata, while these 

 were yet moist, and were intermittingly exposed, wet, to the air, 

 and covered up. They are, therefore, among our best records 

 of the ancient water levels of the continents. 



In a discussion which arose, concerning the possible modes in 

 which the small round imprints, usually ascribed to rain drops, 

 may have been produced, Prof. H. D. Rogers threw out the sug- 

 gestion, that they may perhaps have been formed, in certain 

 cases at least, by a sprinkling of spray from waves breaking 

 on a beach. That these so-called rain spots should so usually 

 accompany those surfaces which bear other independent evi- 

 dences of a shore origin, is an argument in favor of this view, 

 while the fact that the insulation or sparseness of the spotting is 

 almost invariably such that only a very light and most transient 

 sprinkling of rain could produce it, militates, he thought, against 

 the rain hypothesis. The objection is all the stronger, too, when 

 we reflect, that in those early periods of the world, the atmos- 

 phere was, from every evidence, more humid than it is at pres- 

 ent, and the rains necessarily, therefore, were heavier. 



The President observed that he was disposed to consider them 

 the result of rain. The impressions are very generally found, 

 their number is immense, and they are vertical, oblique, single, 

 double, treble, &c., precisely the characters of rain-drop impres- 

 sions in recent clay, in specimens from the Connecticut River, 

 now in his possession. 



Prof. Wm. B. Rogers remarked, that he had made experiments 

 to determine the effect of raindrops on soft plaster. He found 

 that a slight fall of rain produced a very striking resemblance to 

 the fossil impressions, but that a further action of the shower 



