A study of the mineralogical and lithological distribution and association of clay minerals by the X-ray diffraction powder method is described. The geologic work was done at Golden, Colorado, where a complete section across the Upper Cretaceous Laramie formation was mapped, measured, and sampled in detail.

It was found possible to subdivide the Laramie into three stratigraphic intervals based on the clay-mineral assemblages identified by X-ray patterns. The upper formation boundary was confirmed, and the lower boundary was raised 65 feet from interpretation of the X-ray data.

X-ray terminology and theory are presented briefly only where definitions are needed. The X-ray laboratory techniques for geological work are described.

The X-ray and geologic data are evaluated and integrated. Stratigraphic distribution of the clay minerals--laterally as well as vertically--was found to transect lithologic facies boundaries. The lithologic column of the measured section with some X-ray patterns made from the rock samples is shown. Possible uses of X-ray diffraction as a well-logging technique are presented.

It is concluded that X-ray diffraction can be used to advantage by geologists, particularly where mixtures of clay minerals and other fine sediments can not be handled by other methods.