Clay minerals were collected from shales and clay deposits in New England and Eastern Canada ranging in age from Precambrian to Recent. The collection was made to include representative clay minerals of each district, geological period, and environment. Fifty-six samples were selected for detailed petrographic and X-ray study. The potash clay minerals, or hydrous micas, and chlorite are the abundant clay minerals in the marine shales examined. The hydrous micas, chlorite, or vermiculite are the abundant clay minerals in the varved clays of nonmarine origin and clays containing marine fossils of Quaternary age. Clay from glacial till also contains potash clay minerals and vermiculite. The source material had a greater influence on the clay-mineral composition than the environment in which the clay minerals were deposited. The clays and shales that contain abundant kaolinite were apparently deposited under nonmarine conditions. They were eroded from kaolinite clays formed by surface weathering or by hydrothermal replacement. Kaolinite deposits attributed to these processes occur in this region.