Geological Survey Professional Paper Volume 346

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1987* Excerpt: ...carbonate content of the rock. They include the forms termed "molar-tooth" structures by Daly (1912, p. 7276) but with infinite variety in the details so that many have no resemblance to molar-tooth markings. The rock consists of carbonate, and quartz with some sericite. In most beds individual grains of the major constituents are a few thousandths to a few hundredths of a millimeter in diameter, and accessory minerals are in such minute grains and small amounts that they were not determined. Microscopic irregularities in texture, related to the molar-tooth and similar structures so conspicuous in outcrops, are plentiful (fig. L4 and ('). Well-defined oolites are not common, but many of the rocks seem to contain recrystallized oolites. Where oolites are preserved some are roughly elliptical in section, 1 to 2 mm long, and retain no internal structure. Other oolites are circular in section and have well-preserved concentric structure within them (fig. 3(7). The two varieties may occur in the same rock. Some of the round oolites are broken and others are invaded in their outer layers by grains of clastic quartz. Most of the round oolites are less than a millimeter in diameter and are themselves components of pebblelike masses embedded in the fine-grained limestone (fig. 35). While the predominant constituent of the Siyeh limestone is carbonate, cryptocrystalline silica is common, clastic grains of quartz are discernible locally and some strata contain minerals of micaceous habit. The last mentioned are largely sericite but include some montmorillonite and illite. Stromatolites are present throughout the Siyeh limestone of Glacier National Park and may be more abundant and well preserved there than in other parts of western Montana. However, they ha...