The basis for his estimate of the age of the cypress basins was the computed age of the trees of the fourth level, ten feet in diameter and probably reaching 5,700 years.[138] Sir Charles Lyell in a later work, though still adhering to his former estimate of the time required in which to form the delta, cannot accept Dr. Dowler’s great antiquity for the remains.[139] The question in hand of course involves the question of the antiquity of the deposit where the skeleton was found, which is well-nigh identical with the vexed question of the age of the delta. The very diversity of opinion on this subject precludes the possibility of its consideration here. We will content ourselves by citing two estimates in addition to those already given. Professor Edward Hitchcock calculated that the entire delta embraced a bulk of matter equal to 2,720 _cubic_ miles, for the deposit of which he thought 14,204 years necessary.[140] Humphries and Abbot think that both the area and thickness of the deposit have been overstated, and instead of 30,000 square miles for the former, they claim only 19,450. As to the latter, they estimate the thickness of the alluvial matter as but twenty-five feet on the river banks along the St. Francis swamp; thirty-five along the Yazoo swamp, and continuing of uniform thickness to Baton Rouge; while the artesian well at New Orleans showed it in that locality to reach a point forty feet below the level of the Gulf. These authors base their calculations as to the age of the deposits on the following ascertained facts: the total yearly contributions of the river equal a prism two hundred and sixty-eight feet in height, with a base of one mile square; two hundred and sixty-two feet is the supposed mean yearly advance of the river; the original mouth of the Mississippi was near the afflux of the Bayou Plaquemine, and has hence progressed two hundred and twenty miles since it began to empty its deposits into the Gulf. Supposing these data to be correct, they estimate that only four thousand four hundred years have elapsed since that period.[141] This would give the skeleton alluded to a comparatively recent origin. We are inclined to believe that the above estimate assigns a period for the formation of the delta as much too short as that of Sir Charles was too long. As to the antiquity of the skeleton, probably Dr. Foster’s solution of the question is as near correct as any that ever may be proposed: “Thus, then, with these carefully-observed computations before us, we are not prepared to accept the high antiquity assigned by Dr. Dowler to the human remains found beneath the surface at New Orleans. What he regards as four buried forests which once flourished on the spot, may be nothing more than driftwood brought down the river in former times which became embedded in the silts and sediments which were deposited on what was then the floor of the Gulf.”[142]