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to admit of their study under the microscope. The parts usually exhibiting internal structure are stems, branches, roots, and other normally hard organs, yet in exceptional cases every part of the plant, including the leaves, buds, and flowers, are so perfectly preserved that they may be as successfully studied as though living. An example of this kind is afforded by the Carboniferous groups of Cordaites, found in a state of silicification in central France.

Plants that are so preserved as to retain their internal structure, admit of closer study and characterization than is usually attained for other plant organs. So valuable is this method that Professor W. C. Williamson, the distinguished English paleobotanist, was led to say^[1] "that no determinations respecting fossil plants can have much absolute value save such as rest upon internal organization; that is the basis upon which all scientific recent botany rests, and no mere external appearances can outweigh the positive testimony of organization in fossil types." Therefore, when it is possible to obtain plant remains with the internal structure preserved, it may be safely set down that they will afford valuable and reliable data for stratigraphic identification.

The study of the internal structure of fossil plants is yet young in North America, and while a broad field remains for future investigation, enough has already been accomplished to show its value. A few examples may be cited:

In 1888, Araucarioxylon Arizonicum was described from the Trias (Shinarump group of Powell) of New Mexico. The same species has been found characteristic of the Trias of North Carolina^[2] and of the copper mines near Abiquiu, New Mexico.^[3]

In his paper on the geology of Skunnemunk Mountain, Orange county, New York,^[4] Professor C. S. Prosser relies upon