20 THE MISSO VBI MO UND B UILDEBS. 



proximity of the mounds sball be disturbed by an advancing civilization 

 that implements, now hidden by the superincumbent vegetable mold, will 

 be found in their immediate vicinity. 



As to the age of the mounds themselves, independent of the evident 

 antiquity of the implements found in their neighborhood, they bear inter- 

 nal evidence of very great age, as well from the type of the mysterious 

 race found resting in them, as from the evidence afforded by their internal 

 structure. Careful observation failed to disclose in or beneath any one of 

 them the least trace of local vegetable mould, while overlying them, on their 

 external surface, the vegetable mould has attained as great thickness as is 

 found m the surrounding country. The trees on the mounds are of the same 

 species as those in the forest environing them, and have attained as great 

 size and age. If there had been a vegetable mould removed at the base of 

 the mounds before their erection, there should be some evidence remaining 

 of its presence, either in or immediately around them ; but no such evidence 

 exists. If we consider the fact that the implements in the neighborhood 

 are found imbedded in the loess, and the farther fact that the mounds rest 

 upon and are entirely composed of this formation, with the exception of the 

 accumulation at the surface, which has taken place certainly subsequently 

 to their erection, we can scarcely escape the conclusion that they must have 

 been built during the time the loess deposit was yet going on, or very soon 

 after its completion, and before a perceptible vegetable mould had been 

 formed. Prof Aughy, in his (geological Eeport of Nebraska, estimates the 

 time required for the deposit of 200 feet in thickness of loess at 20,000 

 years. This is perhaps a liberal estimate. The greatest thickness of the 

 loess here does not exceed 100 feet, and the greatest thickness on the high- 

 est points, such as those upon which the mounds are erected, does not exceed 

 20 feet. Supposing 10,000 years for the deposit of 100 feet, 2,000 years 

 wauld be required for the deposit of 20 feet ; so that there would intervene 

 8,0i00 years between the last of the upper and the last of the lower deposit. 

 After the recession of the lake waters, 8,000 years, no doubt, would give 

 ample time for the production of a luxuriant vegetable growth, and the 

 accumulation of a very perceptible thickness of vegetable mould. 



Now, if it be true that the mounds were erected before the accummula- 

 tion of a perceptible quantity of mould, it renders the high probability 

 almost into a certainty that they were constructed before the completion of 

 the loess deposit, and while a lake of considerable magnitude still laved a 

 shore line extending north along the Line Creek valley and along the bluffs 

 immediately under the mounds, that our mound builders were dwellers on 

 the shore of a lake, which, like themselves, long since has passed away, 

 leaving evident traces, enwrapped in mystery, of a past existence. 



The great antiquity to which this necessarily leads us is not inconsistent 

 with the immunity of the bones from decay, when we consider their evident 

 protection from moisture, and the vicissitudes of the seasons, in the situation 

 in which they are found, and when we consider their present chemical con- 



