OUTLINE OF THIS VOLUME. XVII 



Chapter IX. Certain basaltic and other rocks associated with the andesitic breccias and 

 basalt flows have a considerable content of orthoclase in microscopic crystals, and a comparatively 

 hio-h percentage of potash. They occur as lava flows and as dikes in various localities within the 

 Park. According to their chemical and mineral composition they have been classed as absarokites, 

 shoshonites, and banakites. 



Chapter X. The rhyolites of the Park are almost wholly extrusive lavas of very uniform compo- 

 sition, but having a wide range of color, texture, and' megascopic habit. The appearance of the rhy- 

 olite in the field, and the microscopical characteristics of phenocrysts, spherulites, lithophysie, and 

 groundmass, are described in detail. The different modifications of crystallization, besides the lami- 

 nation and formation of pumice, are referable to heterogeneity of the molten magma, especially with 

 reference to the amount of vapor contained in it. Examples of intermingled basalt and rhyolite are 

 described, in which the basalt appears to have been inclosed and partly melted by the rhyolite. 



Chapter XI. The recent basalts overlie the rhyolite in most instances, but are found beneath it, 

 and also between older and younger sheets of rhyolite in several localities. These basalts are distin- 

 guished from those associated with the early and late basic breccias by being ophitic and nonpor- 

 phyritic for the most part. 



Chapter XII. This chapter describes the Paleozoic fossils known to occur in the Yellowstone 

 National Park and the Absaroka Range. It is divided into two sections, the first treating of the Cam- 

 brian species and the second of the Devonian and Cfirboniferous species. Both Flathead and Gallatin 

 formations have yielded a small but characteristic fauna. From the Cambrian 21 species in all have 

 been obtained, several of which are new to science and described here for the first time. No fossils 

 of irndoubted Silurian age have been obtained, although the beds carry imperfect and partially oblit- 

 erated organic forms. The Three Forks limestone has furnished a well-recognized Devonian fauna. 

 From the Madison limestone a varied fauna has been collected, but belonging wholly to the Lower 

 Carboniferous period. 



Chapter XIII. The Mesozoic fossils obtained from the Yellowstone National Park were found in 

 the Gallatin Range near Electric Peak, Teton Range, in the neighborhood of Wildcat Peak and 

 Huckleberry Mountain, and from the Cretaceous ridges in the southern end of the Park and Yellow- 

 stone Forest Reserve. The Meaozoio strata have yielded 78 species of invertebrates, of which one is 

 from beds supposed to be of Triassic age, 46 are Jurassic, and 31 are Cretaceous. The fossils obtained 

 were mainly from the Ellis formation of the Jura and the Colorado of the Cretaceous. The Jurassic 

 fossils form much the largest and most prominent part of this collection, and in number of species it 

 compares favorably to the Jurassic of other parts of the Rocky Mountains. 



Chapter XIV. The Mesozoic fossil flora of the Yellowstone National Park is confined to the 

 Laramie sandstones of the Cretaceous and is found on Mount Everts, near Mammoth Hot Springs, and 

 at the base of Pinyon Peak near the head of Wolverine Creek. The flora from this latter locality has 

 been designated the Wolverine Creek flora. The Tertiary flora is very varied and possesses great 

 biological interest. It is a rich flora, and on comparing it with the living flora it becomes apparent 

 that great climatic changes must have taken place since the close of Miocene time to have made these 

 changes iu plant life possible. It is found at numerous localities associated with the breccias and 

 silts of the igneous rocks of the Absaroka Range. It is found in the early acid breccias, in the early 

 basic breccias, in the late acid breccias, and in the late basic breccias, whore the mnds and silts 

 furnish a soil favorable for a vegetable growth. The most interesting locality as regards number of 

 species and mode of occurrence is the well-known Fossil Forest of Specimen Ridge. The Tertiary 

 fossil flora embraces about 150 forms that have been distributed among Xi natural orders. This fossil 

 flora is illustrated by forty-five plates. 

 MON XXX n, PT II II 



