The Green River Formation of Colorado, Wyoming, and Utah consists of an organic rich shale or marlstone. This deposit consists of varying amounts of soluble organic material, insoluble organic material, and minerals. The mileral composition depended upon the amounts of soluble and insoluble minerals washed into the basin lakes and upon conditions which caused precipitation of minerals from the aqueous phase. Precursors for organic material consisted of algae which grew profusely in the saline lakes, and the plant sports and pollen grains which were wind borne into the lakes. The amount of organic material remaining in the sedimentary shale depended upon the amount of accumulation, preservation, and alteration of the original precursor organic material.