78 NATURAL SCIENCE. Feb.. 



of structures requiring calcareous salts are being rapidly developed. 

 The larval stereom, therefore, which has been gradually accumulated 

 from the earliest embryonic stages, may be regarded as reserve 

 material for building up the future complex skeleton of the young sea- 

 urchin. A mere accumulation of such reserve material might con- 

 ceivably have had a pernicious effect on the larva, but, as things are, 

 the reserve stereom has become essential to the existence of the 

 larva itself, since it has assumed the most suitable form possible for 

 facilitating the flotation of the larva in the sea. 



The Duration of Niagara Falls. 



In an interesting paper, contributed to the American Journal of 

 Science for December, Mr. J. W. Spencer discusses the history and 

 prospects of the Niagara Falls. The paper is illustrated by an 

 excellent set of charts and maps, and should be valuable to the 

 physiographer and geologist. We reprint the conclusions to which 

 he comes : — 



" The computation of the age of the Niagara river, — based upon 

 the measured rate of recession during 48 years ; upon the changing 

 descent of the river from 200 to 420 feet and back to 320 feet ; and 

 upon the variable discharge of water from that of the Erie basin only, 

 during three-fourths of the life of the river, to afterwards that of all the 

 upper lakes, — leads to the conclusion that the Niagara Falls are 

 31,000 years old and the river of 32,000 years' duration; also that the 

 Huron drainage turned from the Ottawa river into Lake Erie less 

 than 8,000 years ago. Lastly, if the rate of terrestrial deformation 

 continues as it appears to have done, then in about 5,000 years the 

 life of Niagara Falls will cease, by the turning of the waters into the 

 Mississippi. These computations are confirmed by the rate and amount 

 of differential elevation recorded in the deserted beaches. It is further 

 roughly estimated that the lake epoch commenced 50,000 or 60,000 

 years ago, and there was open water long before the birth of Niagara 

 in even the Ontario basin, and that under no circumstances could 

 there have been any obstruction to the Ontario basin, if even then, 

 later than the end of the Iroquois episode which has been found to 

 have ended 14,000 years ago." 



A New Bone-Cave. 



In a recent letter to Sir Henry Howorth, Mr. H. C. Mercer, of 

 the University of Pennsylvania, announces the discovery of an in- 

 teresting bone-cave in that State. It was discovered during blasting 

 operations, in a limestone quarry, and is close to a similar cavern which 

 was opened in 1870, and some of the remains from which were 

 described by Cope. The whole is filled to the roof with a stratified 

 deposit, consisting of fragments of limestone, clay, and sand, in which 

 numerous bones occur. These are all broken, and are said to include 

 remains of mastodon, tapir, sloth, peccary, ox, bear, and, probably, of 

 birds. No remains of man, fishes, or mollusca have yet been met 

 with. 



