History and Comprehensive Description of Loudoun County, Virginia by James William Head
page 45 of 250 (18%)
page 45 of 250 (18%)
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fine white marble are seen; with rare exceptions also pebbles of
Catoctin schist and quartz occur. They are embedded in a red calcareous matrix, sometimes with a slight admixture of sand. As a rule the entire mass is calcareous. The conglomerate occurs, as has been said, in lenses or wedges in the sandstone ranging from 1 foot to 500 feet in thickness, or possibly even greater. They disappear through complete replacement by sandstone at the same horizon. The wedge may thin out to a feather edge or may be bodily replaced upon its strike by sandstone; one method is perhaps as common as the other. The arrangement of the wedges is very instructive indeed. The general strike of the Newark rocks is a little to the west of north, while the strike of the Catoctin Belt is a little to the east of north. The two series, therefore, if extended, would cross each other at an angle of 20 to 30 degrees. The conglomerate wedges are collected along the west side of the Newark Belt and in contact usually with the Weverton sandstone. The thick ends of the wedges along the line of contact usually touch each other. Going south by east the proportion of the sandstone increases with rapid extermination of the conglomerate. The thin ends of the wedges, therefore, resemble a series of spines projecting outward from the Catoctin Belt. The result of weathering upon the conglomerate is a very uneven and rugged series of outcrops projecting above the rolling surface of the soil. The ledges show little definite stratification and very little dip. The topography of the conglomerate is inconspicuous and consists of a slightly rolling valley without particular features. It approaches |
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