142 THE JOURNAL OF GEOLOGY. 



I have come by calculating from the mean depth of neolithic 

 finds in Norwegian peats, but this computation has not quite so 

 much importance, though the fact that the generally adopted 

 archeological chronology agrees as well with geological estimates 

 certainly has some weight. 



I shall recall the fact that calculations on the length of post- 

 glacial time based on the receding Niagara, St. Anthony Falls, or 

 the Michigan lake shore, on boulder pedestals in Scotland, the 

 denudation of the Somme, the Plum creek, or the Raccoon valley, 

 deposition of the Tiniere or the Rhone, etc., delta, the thickness of 

 glacial clay in New Hampshire and in Sweden, the rate of growth 

 of peat in North America and Ireland, the atmospheric waste of the 

 Parallel roads in Lochaber, the depth of some ancient neolithic 

 finds, that all these give numbers of about the same value, 5,000 to 

 12,000 years. Doubtful as some of these chronometers may be, 

 all fair chances are against any supposition which differs in any 

 considerable degree from those of about thirty iiidependent esti- 

 mates I have got together. With full regard to a legitimate cal- 

 culation of probabilities, it may be predicated that the number of 

 7,000 to 10,000 years is as nearly an exact estimate of the dura- 

 tion of post-glacial time as can ever be expected. 



It is now tempting to try a comparison between the subglacial 

 and the epiglacial terraces and lakes in Norway. When the 

 much greater eroding force of the epiglacial glaciers is properly 

 reduced, I do not think it can be very much at variance with the 

 truth to compute the epiglacial period to be between five and 

 ten times the duration of the subglacial, the smaller number being 

 somewhat more probable. We would then get 10,000 to 20,000 

 years for the epiglacial period and perhaps 15,000 to 25,000 for the 

 whole deuteroglacial time. For the interglacial period, the Norwe- 

 gian geology cannot as yet give any reliable measure but the depth 

 of the aspen and pine layers in the Danish peats as compared with 

 the post-glacial oak and birch layers does answer very well to the 

 American estimates of one and one-half to two times the duration 

 of post-glacial time — let us take about 15,000 years. We may 

 next compare the proteroglacial fjords with the epiglacial lakes 



