22 THE POPULAR SCIENCE MONTHLY. 



land ranges, crept southward to Long Island and northern New 

 Jersey, and heaped up the eastern extension of the terminal mo- 

 raine, and, as it melted, gave origin to the Champlain deposits 

 of the New England rivers and to certain distinctive aqueo- 

 glacial gravels, of which those of the Delaware at Trenton are 

 the type. 



The lower lacustral deposits of the Great Basin, the aqueo- 

 glacial deposits of the Mississippi Valley, and the ancient deltas 

 of the Atlantic slope are correlated, partly because (1) each attests 

 a great and similar climatal episode, because (2) it is evident 

 that each of these episodes was so extreme as to affect the entire 

 breadth of the continent, and because (3) there are no indications 

 among American geologic deposits of other episodes with which 

 these might be confused ; the upper lacustral beds of the Great 

 Basin, the upper glacial and aqueo-glacial deposits of the Missis- 

 sippi Valley, and the glacial deposits of the Atlantic slope, are 

 correlated upon similar grounds ; and the harmony among the 

 various records gives cumulative proof of the accuracy of each. 



By these researches of the last decade the earlier conceptions 

 of Quaternary history are greatly expanded, and the hitherto ob- 

 scure relation between the Tertiary and Quaternary is made clear. 

 Where they contain vertebrate fossils, the earlier and even the 

 later of these deposits are, it is true, referred to the Pliocene by 

 paleontologists, while physical geologists refer the entire series 

 to the Quaternary; but this discrepance is one of classification 

 only, and in no way affects the phenomena classified. 



The sequence of events made out independently in the three 

 widely separated regions may be depicted as in the accompanying 

 diagram (Fig. 1), representing the temperatures and land-altitudes 



TERTIABY aUATERNAOY 



DCISTENCC or MAM DOUBTFUL PALEOLITHIC MAN • 



Fig. 1.— Graphic Repeesentation op Climate and Changes in Altitude op the Land. 



during late Tertiary and Quaternary time. By such a chrono- 

 graph alone is it possible to accurately measure the antiquity of 

 paleolithic man. Marsh has well shown that only long seons can 

 be measured by plant fossils, that somewhat shorter periods may 

 be measured by the records of invertebrate life, and that the ver- 

 tebrates afford by far the most delicate of the paleontologic time- 

 measures ; but the swing of even the vertebrate life-pendulum is 



