This transportation theory is based on several types of evidence. In the first place, the logs have been stripped of much of their original roots and limbs, and practically all of the bark has disappeared. The logs present a worn appearance, an indication of having received rough treatment. Also, very few traces of cones or foliage have been located, although the fossil remains of more than 30 species of fragile ferns, cycads, rushes, and other plants that grew in the marshes of the ancient flood plain have been found. The direction of the original drainage into this area has been established by tracing the source of the Permian gravels which are deposited here. The deposition of these sediments over the plain continued until a layer about 400 feet thick was built up during the centuries. This deposit is now known geologically as the “Chinle Formation.” One of the principal materials found in the Chinle is Bentonite, originally a volcanic ash which the streams brought. It has since decomposed into a clay-like soil which is very porous and spongy and which readily absorbs water and expands. When becoming very wet, it turns into a bluish mud and is washed away. Erosion of this Bentonite and other materials deposited with it forms the badlands area now seen on portions of the monument and in the Painted Desert. During the ages when the original layers of mud, sand, and silt were being deposited, many of the logs were washed in and buried at various levels with this Chinle material. While all of this was slowly taking place, the land mass over this part of the continent was gradually subsiding. It continued to settle during the next geological period of millions of years, and layer after layer of sediments were washed in and deposited on top of it. Then during the next geological (Cretaceous) period, a long arm of a sea flooded this part of the country. Marine deposits accumulated on the bottom of the sea until finally the Chinle Formation containing the buried logs was covered by 3,000 feet or more of other deposits. At the close of Cretaceous time, about 60 million years ago, uplift of the present Rocky Mountain system commenced. The basin in which the Petrified Forest lay buried rose with it. This gradual rising movement has continued intermittently nearly to the present time.