Page:The Journal of geology (IA journalofgeology21894univers).pdf/392

Large numbers of huge vertebrate remains, only known from "The Laramie of Wyoming," fortunately have fragments of fossil plants adhering to them, from the study of which important light will be thrown on the age of the beds in which they are contained.

Along the Missouri river in the vicinity of Great Falls, Montana, there is exposed a considerable thickness of mainly brown, sandstone rocks. They have been eroded by the river into more or less of a cañon, and are the material in which the falls have been developed. From their lithologic appearance, but mainly upon stratigraphic grounds, these rocks have been referred by geologists to the Dakota group. On going down the river they disappear under the Fort Benton shales, and are consequently in the stratigraphic position of the Dakota, but the recent discovery of plant-beds near Great Falls has shown the impossibility of such reference. The plants are typically lower Cretaceous, and have been positively identified by Newberry with the Kootanie of Canada. By this a part at least of the so-called Dakota goes to the lowest Cretaceous.

In a similar way a part of the supposed Dakota of the Black Hills has been shown by Professor Ward,^[1] purely on paleobotanical evidence, to belong to the lower Cretaceous.

The Foreman beds in the Taylorville region, Plumas county, California, were determined to be of Rhætic age from the fossil plants, a determination agreeing perfectly with the stratigraphy.^[2]

The copper mines near Abiquiu, New Mexico, were identified as Triassic by the plants found in and about the roof of the openings.^[3]

The employment of fossil plants in practical mining exploitation is well shown by the results obtained by Grand' Eury and Zeiller in Southern France.

In the Department of Gard the mining of coal is one of