22 



emergence of the land, during which rise the ridges before alluded 

 to were produced, and the boulder formation partially denuded. He 

 also endeavours to show, how during this last upheaval the diflferent 

 lakes may have been formed in succession, and that a channel of the 

 sea must first have occupied the original valley of the Niagara, 

 which was gradually converted into an estuary and then a river. The 

 great Falls, when they first displayed themselves near Queenstown, 

 must have been of moderate height, and receded rapidly, because the 

 limestone overlying the Niagara shale was of slight thickness at its 

 northern termination. On the further retreat of the sea a second 

 fall would be established over lower beds of hard limestone and 

 sandstone previously protected by the water ; and finally, a third fall 

 would be caused over the ledge of hard quartzose sandstone which 

 rests on the soft red marl, seen at the base of the river-cliff at Lewis- 

 town. These several falls would each recede further back than the 

 other in proportion to the greater lapse of time during which the 

 higher rocks were exposed before the successive emergence of the 

 lower ones. Three falls of this kind are now seen descending, a 

 continuation of the same rocks on the Genesee River at Rochester. 

 Their union, in the case of the Niagara into a single fall, may have 

 been brought about in the manner suggested by Mr. Hall*, by the 

 increasing retardation of the highest cataract in proportion as the 

 uppermost limestone thickened in its prolongation southwards, the 

 lower falls meanwhile continuing to recede at an undiminished pace, 

 having the same resistance to overcome as at first. 



Mr. Lyell considers the time occupied by the recession of the Falls 

 from the Whirlpool to be quite conjectural, but assigns a foot rather 

 than a yard a year as a more probable estimate ; thus he shows the 

 Mastodon, found on the right bank near Goat Island, though asso- 

 ciated with shells of recent species, to have claim to a very high an- 

 tiquity, since it was buried in fluviatile sediment before the Falls had 

 receded above the Whirlpool. 



" Notice on a Suite of specimens of Ornithoidicnites, or foot-prints 

 of Birds on the New Red Sandstone of Connecticut." By Gideon 

 Algernon Mantell, LL.D., F.R.S. 



These specimens were accompanied by a letter fromDr. JamesDeane 

 of Greenfield, Massachusetts, the original discoverer of the Ornithoi- 

 dicnites, of which more than thirty varieties had been found, bearing 

 a striking resemblance to the foot-prints of birds. In this letter Dr. 

 Deane gives an account of his discovery of the impressions eight or 

 nine years ago, and which he then communicated to Professor Hitch- 

 cock. He remarks, that " the footsteps are invariably those of a 

 biped, and occur on the upper surface of the stratum, while the cast 

 or counter-impression is upon the lower. In some instances we may 

 follow the progress of the animal over as many as ten successive 

 steps." He has seen a course of steps twelve inches in length by 

 eight in breadth, extending several rods. The intervening space 



* Boston Journ. of Nat. Hist., 1841. 



