INTRODUCTION AND ACKNOWLEDGMENTS Over many years the senior author, assisted by other members of the United States Geological Survey, has accumulated many brachiopods from the Ozarkian and Canadian periods. In 1931 the junior author joined in the study of these collections. Before the study was undertaken, about 170 species of brachiopods representing about 24 genera were known. The authors have added 32 genera and have increased the number of species to 319. In addition to the above mentioned specimens a large collection was studied which was made by C. D. Walcott. All regions of Ozarkian and Canadian strata known in North America, except Newfoundland, are represented in the collections. It is a pleasure to acknowledge gratefully the kind assistance received from the Geological Society of America through a grant from the Penrose Bequest. This grant enabled the authors to have the illustrations prepared and permitted the junior author to visit the National Museum of Canada in order to study Billings’ brachiopod types from Lévis, Quebec. Special thanks are due Dr. Edwin Kirk of the United States Geological Survey who generously loaned large collections of brachiopods from the Great Basin and adjacent country. The authors are also indebted to Dr. Charles Butts, formerly of the United States Geological Survey, who furnished a number of the specimens from the southern Appalachians. Dr. Josiah Bridge of the United States Geological Survey and Mr. It. D. Mesler assisted in many ways and supplemented the collections by fine material. Acknowledgments are also due Dr. E. . . .

Extract from beginning of chapter: EUREKA, NEVADA During May and June [1880], I worked as a temporary assistant to Hague on the United States Geological Survey, and on the first of July, I received my appointment as assistant geologist and felt duly elated. It had been King's plan that Hague should have charge of the Division of the Pacific Coast with headquarters in San Francisco, and that he should study the volcanoes of that region beginning with Lassen Peak. But it seemed advisable that his first work should be of a more utilitarian character, so he was commissioned to investigate the geology of the Eureka Mining District in central Nevada. 1 Leaving New York on the evening of the 16 th of July, we were joined in Utica, New York, by a tall, slender, red-whiskered young man who was said to be a promising paleontologist, who had already made a reputation out of his studies of Trenton trilobites, and who had spent the previous season in the Grand Canyon of the Colorado [River]. The next morning, I made the acquaintance of Charles D. Walcott 2 and commenced a lifelong friendship full of interesting experiences and pleasant memories. At the end of the sixth day, we reached Eureka, after a journey, which, for a young geologist, became more and more fascinating and instructive as it proceeded. Nowhere can one see geological structures on a grander scale or in more easily comprehended exposures than in the barren ranges of the Great Basin desert! Its simplicity as well as its nakedness

Studies of middle Paleozoic history in western America have long been delayed. For the past 50 years efforts of stratigraphers on the Pacific Coast have been devoted largely to investigation of Mesozoic and Cenozoic strata, good outcrops of which are found in the vicinity of several western centers of geologic research. Moreover, growing importance of geology in the petroleum industry has given vital encouragement to study of the younger strata. Remote and somewhat difficult of access, the Paleozoic areas have received but small share of the attention they justly deserve. Conclusions regarding the older systems have thus remained speculative in absence of field evidence which would permit a scientific attack. In the eastern States, particularly New York, even a century of progress in Paleozoic stratigraphy still leaves many unsolved problems. It is not surprising then that knowledge of some Paleozoic systems in the west is still insufficient to make possible even satisfactory definition of the problems themselves. While the western Cambrian faunas have become reasonably well known through the vigorous collecting program of Charles D. Walcott and his associates, and while the Carboniferous strata and faunas have received a fair amount of study, the intermediate systems have until recently remained almost untouched since the days of federal exploring expeditions in the western territories. Following the exploratory phase of western geology in the latter half of the past century, study of western middle Paleozoic stratigraphy was for the most part incidental to mapping programs in mineralized regions where the structure is . . .