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Insoluble residues and calculated calcite and dolomite contents of representative samples of carbonate rocks from Upper 4. Abandoned and little-used stratigraphic names formerly applied in Kentucky to exposed strata of Ordovician age above the Lexington Limestone -

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Crossbedding in sandstone units is the most conspicuous sedimentary structure of the Potomac Formation in Fairfax County, Virginia. Most sets of crossbeds are a few feet thick and several feet wide and tens of feet long. Trough sets are dominant, but planar sets are also common. Dip directions of crossbeds show great variation, though westerly dips are sparse. The averages (resultant vectors) of crossbedding dip-directions measured at 33 localities do not show significant differences according to their geographic or stratigraphic distribution. The average dip-" direction of the 292 crossbeds measured is N. 85° E. The data suggest that the depositional slope was easterly in Fairfax County throughout the time of deposition of the Potomac Formation. Major sand bodies, potential aquifers of the formation,are probably elongated along easterly trends.

More than 70 breccia pipes lie along northwesterly trends near Spanish valley in Grand and San Juan Counties, a few kilometers southeast of Moab, Utah. The structures generally are roughly oval in plan and only several tens of meters in diameter, but are inferred to extend downward about 1,000 m. The pipes contain a breccia that has been dropped as much as several hundreds of meters by solution collapse. Much sandstone in the breccia has been decemented and in places has flowed, as shown by foliation and sandstone dikes. Contacts of the breccia and country rock are sharp. The country rock is unaltered. The structures apparently formed in the Tertiary and may be contemporary with igneous intrusions of the nearby La Sal Mountains. The breccia pipes probably result from solution of deeply buried salts and carbonate rocks by migrating waters heated by the igneous intrusions, followed by upward stoping of younger strata. The breccia pipes of Spanish valley and environs are not known to be mineralized, but they resemble uranium-and copper-bearing breccia pipes elsewhere on the Colorado Plateau.