330 LECTURE XI. 



deposits), we obtain 1,500 years for tlie era of aquatic plants 

 until the cypress era. Supposing ten feet to represent the 

 size of one generation of trees, we obtain a period of 6,700 

 years as the age of the oldest trees now growing in the basin, 

 for they measured from ninety-five to one hundred and twenty 

 rings of annual gr^owth to an inch ; and according to the lowest 

 ratio, a tree of ten feet in diameter will yield 5,700 rings of 

 annual growth. Though many generations of such trees may 

 have grown up and perished in the delta of the Mississippi, 

 Dr. Dowler, to avoid all cavilling, has only assumed two suc- 

 cessive growths, including that now standing : this gives for 

 two cypress generations the age of 11,400 years. 



The maximum age of the oldest trees on the Hve-oak bank 

 is estimated at 1,500 years ; one generation only is counted. 

 Thus we obtain the following data : — ■ 



Era of aquatic plants ... - 1,500 years. 

 Era of cypress basin .... 11,400 „ 

 Era of live-oak platform .... 1,500 „ 



Total period - - 14,400 



Each sunken forest must have had a period of rest and 

 gradual depression, estimated as equal to the era of live-oaks, 

 which of course occurred only once in the series. We then 

 certainly keep within the limits of probability in assuming each 

 period of elevation to have been equivalent to the one above 

 arrived at, and as there were at least ten such changes we reach 

 the following result : — 



Last emergence as above .... 14,400 years. 

 Ten elevations and depressions, each 

 equal to the last emergence ... 144,000 „ 



Total age of the Delta . 158,400 



In the excavation of the gas works, burnt wood was found 

 at the depth of sixteen feet, and at the same depth the work- 

 men found the skeleton of a man. The skull lay beneath the 

 roots of a cypress tree belonging to the fourth forest below the 

 surface. It was in good preservation, but the other bones 

 crumbled into pieces on being touched. The cranium no doubt 

 belonged to the American type. 



