Detailed petrographic studies of sandstone cores from productive and non-productive structures in the Rocky Mountain region were made to determine not only the physical characteristics of the sandstones but also the nature and distribution of the cementing materials. The sandstones have been divided into two general groups on the basis of the cementing or binding materials: first, those in which the grains are bound together by argillaceous materials; and second, those in which crystalline minerals form the cement or bond. In the first group, effects of mechanical compaction were noted. In the second group, sequence of deposition of cementing minerals was observed. The deposition of quartz, dolomite, and anhydrite, in the order given, is common in some sandstones. In othe s, quartz and calcite are the only cementing minerals, and of these, calcite is the last mineral deposited. Other combinations of these four minerals were observed. Furthermore, sequence of deposition of the same minerals has been established tentatively for the geologic section from the Bell sandstone which is the basal member of the Minnelusa formation (Pennsylvanian) upward through the Mesaverde (Upper Cretaceous) sandstone.

Also presented are some probable effects of crystalline cementing minerals upon pressures existing in oil and gas fields, the probable control exercised by these mineral precipitates upon the movement of fluids in reservoir rocks between areas of cementation and pressure relief, and the relationship of this fluid movement to the migration and accumulation of oil and gas.