Preface: The author of this paper gives a thorough description of a complex of very unusual igneous rocks and associated hydrothermal deposits.

From abstract: This report describes four species of Ostreidae from the Upper Cretaceous of the Gulf region. The zones that the species characterize lie either in the upper part of the Austin chalk or in beds of upper Austin age.

From Introduction: "The recent large increase in gold production from the Alma district has greatly stimulated interest in territory immediately to the east, where many small gold-bearing veins have been discovered. Consequently, as a cooperative project of the United States Geological Survey and the State of Colorado, 7 weeks in 1938 were devoted to renaissance work to determine the origin of the placer gold and the possibilities for discovering valuable lode deposits either near the surface or at depth."

From introduction and acknowledgements: This report is written to supplement and complete the record contained in some fifty district and special reports already submitted, and duplication of material in district reports has been studiously avoided. The data herein contained are largely of a regional type, inclusion of which was not wholly appropriate to the district reports.