CLOSE OP POST-PLIOCENE ADVENT OP MAN. 293 



years which, according to Dr. Andrews, have elapsed 

 since the close of the boulder-clay deposits in 

 America.* I am aware that such a statement will 

 be regarded with surprise by many in England, 

 where even the popular literature has been penetrated 

 with the idea of a duration of the human period 

 immensely long in comparison with what used to be 

 the popular belief; but I feel convinced that the 

 scientific pendulum must swing backward in this 

 direction nearer to its old position. Let us look at a 

 few of the facts. Much use has been made of the 

 " cone " or delta of the Tiniere on the eastern side of 

 the Lake of Geneva, as an illustration of the duration 

 of the Modern period. This little stream has de- 

 posited at its mouth a mass of debris carried down 

 from the hills. This being cut through by a railway, 

 is found to contain Roman remains to a depth of four 

 feet, bronze implements to a depth of ten feet, stone 

 implements at a depth of nineteen feet. The deposit 

 ceased about three hundred years ago, and calculating 

 1300 to 1500 years for the Roman period, we should 

 have 7000 to 10,000 years as the age of the cone. 

 But before the formation of the present cone, another 

 had been formed twelve times as large. Thus for the 

 two cones together, a duration of more than 90,000 

 years is claimed. It appears, however, that this cal- 

 culation has been made irrespective of two essential 

 elements in the question. No allowance has been 

 made for the fact that the inner layers of a cone ara 

 * " Transactions, Chicago Academy," 1871. 



