REMARKS: A sand-dune field created during the Wisconsinan Age, the latest of several periods of glaciation that covered parts of Pennsylvania. Although the Wisconsinan glacier stopped several miles north of the river, large amounts of sediment were carried into the river and deposited on floodplains downstream. The floodplain here is very broad, and the terraces are well developed; wind, sweeping across the lower terraces, picked up silt and sand and deposited them on the upper terraces to the east. At this site the sand has been blown out into parabolic dunes in a dune field that extends about 1.5 miles east of the river. These dunes are U-shaped, and their tails point up wind. This sequence of dunes, created from glacial outwash, is a rare phenomenon of the Wisconsinan Age in Pennsylvania and is not very common in the United States.
REFERENCES: Chase, C. M. [1977], Central Pennsylvania sand dunes, Pennsylvania Geology, v. 8, no. 3, p. 9-12.
REMARKS: The "whaleback" is a unique combination of rock folding, faulting, and weathering that resembles the shape of a whale's back.
The rock sequence in the Bear Valley strip mine is part of the Llewellyn Formation. It consists of conglomerate, sandstone, mudstone, anthracite, and interbedded shale and sandstone or siltstone.
It is geologically significant in that all recognized structural stages of the Allegheny orogeny in the northern Valley and Ridge province are visible at this site. All structural stages are superimposed at one place; progressive deformation and the relative time of formation of joints, rock cleavage, minor folds, faults, and major folds can be proved.
REFERENCES: Arndt, H. H., Danilchik, Walter, and Wood, G. H., Jr. (1963), Geology of the anthracite in the western part of the Shamokin quadrangle, Northumberland County, Pennsylvania, U. S. Geological Survey Coal Investigations Map C-47.
Arndt, H. H., Wood, G. H., Jr., and Schryver, R. F. (1973), Geologic map of the south half of the Shamokin quadrangle, Northumberland and Columbia Counties, Pennsylvania, U. S. Geological Survey Miscellaneous Geologic Investigations Map I-734.
Nickelsen, R. P. (1976), Sequence of structural stages of the Allegheny orogeny, at the Bear Valley strip mine, Shamokin, Pennsylvania, unpublished manuscript, Department of Geology, Bucknell University, Lewisburg, Pennsylvania.