574 THE ICE AGE IJST NORTH AMERICA. 



bottom of this bowl to a depth of twenty-four feet — a cone 

 ninety-six feet in diameter at the base and twenty-four feet to 

 the apex — which would be equal to a deposit of only eight feet 

 over the present surface of the bottom. The question is. 

 Could this have stood with so little change for eighty thousand 

 years ; or even for forty thousand years, if we were to accept 

 Professor Charles H. Hitchcock's estimate of the prolongation 

 of the effects of Croll's period?* Is not the supposition of 

 ten thousand years sufficiently extravagant ? If the close of 

 the great Glacial period be so far back as Mr. Croll estimates, 

 we must believe that sediment would accumulate, in the situ- 

 ation above described, over the surface of the present peat-bog, 

 at the rate of only one inch in a thousand years ; while, if 

 we put the close of this period back ten thousand years, the 

 rate of accumulation would seem to be as slow as our imagina- 

 tion can well comprehend. One hundred inches, which is 

 little more than eight feet, divided into one hundred thousand 

 parts, would be only -001 of an inch ; that is, if this depression 

 has been in existence one hundred thousand years, we must 

 believe that with all the dust there is in the air, and all the 

 soil that would wash down the steep incline of all the sides. 

 and all the vegetable matter growing in and falling into the 

 depression, one thousand years would be required for one inch 

 of sediment to accumulate ! If we reduce this supposed period 

 to 50,000, 25,000, and 12,500 years successively, the time re- 

 quired for the accumulation of an inch of sediment would be 

 proportionally 500, 250, and 125 years. If any one will be 

 at the trouble of dividing an inch into 125 equal parts, he will 

 probably be surprised at the insignificance of the quantity. 

 The slowest rate at which Boucher de Perthes calculates for 

 the accumulation of peat over Roman pottery in the valley of 

 the Somme is three centimetres, or a little over an inch, in a 

 century. 



We do not bring railing accusation against those who, from 

 astronomical considerations, confidently speak of the close of 

 the Glacial period as an event which occurred scores of thou- 

 sands of years ago ; but it is important to know what other 



* " Geology of New Hampshire," vol. iii, p. 327. 



