. Popular science monthly. son, thestate capital. Here is a large field where erosion is actively taking placeat the present time. Throughout the area are scattered logs and frag-ments in varying stages of disintegration. An amphitheater some twenty or twenty-five feet deep and about onehundred and fifty feet in diameter, where the Columbia loam and theLafayette sand have washed away down to the Tertiary formation, offersthe best single exhibit of the logs. At the mouth of the valley the ero- PETRIFIED FOREST OF MISSISSIPPI 469 sion has extended several feet into the Tertiary. There are at lea
. Popular science monthly. son, thestate capital. Here is a large field where erosion is actively taking placeat the present time. Throughout the area are scattered logs and frag-ments in varying stages of disintegration. An amphitheater some twenty or twenty-five feet deep and about onehundred and fifty feet in diameter, where the Columbia loam and theLafayette sand have washed away down to the Tertiary formation, offersthe best single exhibit of the logs. At the mouth of the valley the ero- PETRIFIED FOREST OF MISSISSIPPI 469 sion has extended several feet into the Tertiary. There are at least tenlogs exposed in this amphitheater which vary considerably in color andcomposition. Some of them are almost pure white and apparently con-tain nearly pure silica; others are stained with more or less of foreignmatter. These logs vary in size and preservation and none of them p:esentsthe full length of the original tree. The largest observed is about sixfeet in diameter by twenty feet in length and is of a brown Fig. 5. Petrified Log from Pittsboro, Miss., now on the lawn of Dr. Calvin at the University of Mississippi. Another is four feet at base by about seventeen feet in length. A dark-colored log near by is five feet at base and eleven feet long. Another ina ravine to the east is four feet by twenty feet; and there are still otherlogs and fragments of logs scattered at various points. Most of these logs now rest upon the Tertiary formation and there-fore are slightly displaced; that is to say, the sand of the Lafayette for-mation has washed from beneath them and left them lying upon theTertiary. In several places however in the vertical erosion walls logs areseen projecting from the Lafayette sand some distance above theTertiary. In the accompanying illustration, number four, the line of unionbetween the Quaternary and the Tertiary is distinctly seen running hori-zontally through the middle of the picture. Some distance above this 47o THE POPULAR SCIENCE
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