38 GEOLOGY OF OHIO. 



(b) PROBABLE AGE OF MOUNDS. 



There has not yet been found in one of these structures, under cir- 

 cumstances that put beyond question the fact of its being deposited by 

 the original builders, a single article of such pattern or material as to 

 prove incontestably that it was obtained from Europeans. Reported dis- 

 coveries of this nature are not authenticated ; nothing less can be accep- 

 ted as testimony of a date more recent than 1492. How far back of this 

 time they may have been erected it is impossible to ascertain. Having once 

 settled compactly and become overgrown, there is no further change due 

 to age. Trees on them are of the same size as those nearby; but this 

 proves nothing except that they are older than the timber, which is self- 

 evident, for they would not have been built in the woods. There are 

 few, if any, trees in Ohio four hundred years old ; with an annual growth 

 of one-eighth of an inch of new fiber, a tree in that time will reach a cir- 

 cumference of twenty-six feet. Few varieties of timber but will exceed 

 this rate of increase in the fertile ground where most of these remains 

 occur; in fact they should grow more rapidly on the works than else- 

 where, as these are usually made of the surface earth and therefore furnish 

 more nutriment to the roots. A cypress tree planted in Philadelphia in 

 1808, had in 1892 a height of 120 feet and a girth of twenty-eight feet; 

 this however, is a soft wood and grows rapidly. An elm in Chicago 

 known to be just fifty years old measured eight feet and two inches in 

 circumference, three feet from the ground. 



Growth-rings are not an accurate test of age: it is not unusual for 

 two or three to form in a year. 



The irrational assertion is often made that a mound must be at least 

 five hundred years old for the reason that it is covered with large trees. 

 It has been reserved for a well-known geologist to cap the climax, within 

 a few months, by stating that some mounds are at least a thousand years 

 old, because not only are large trees growing over them, but on the 

 ground are remains of other trees which lived out their period and fell 

 into decay before those now standing had sprung up. This is, in effect, 

 to claim that all trees live five hundred years and no longer; that all trees 

 growing on mounds have reached this age; and that wood in a state of 

 decay will remain exposed to the weather for the same length of time. 

 Absurdity cannot go further. 



The roots of trees extend many feet into the interior of mounds; 

 when they decaj', the casts contain mold, from the roots themselves or 

 settled in from the surface. If successive generations had flourished on 

 them, it would seem mounds would contain a great number of these casts; 

 but they are comparatively few. This gives reason for supposing the 

 mounds do not reach back many centuries. To avoid such conclusion, 

 the opinion ventured by some geologists that until relatively recent time 

 the Ohio Valley was devoid of forests, has been made to support an argu- 



