Detailed petrographic studies of sandstone cores from productive and non-productive structures in the Rocky Mountain region were made to determine not only the

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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 clay products; and second, those in which crystalline minerals form the cementing material. In the first group effects of 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 others, 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 de osition of the same minerals has been established tentatively for the geologic section from the Bell sandstone upward through the Mesaverde sandstone.

Also presented are some probable effects of crystalline cementing materials upon migration and accumulation of oil and gas, upon acid treatment of wells, and upon pressures existing in oil and gas fields.

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