File:Tolchester folio Maryland Plate VII.jpg

English: Plate VII from Tolchester Folio, Maryland, which has the following caption:

CONGLOMERATE IN WICOMICO FORMATION, NEAR BETTERTON, KENT COUNTY.

The Wicomico formation extends below sea level at this point.

The text of the Folio states:

The materials which compose the (Wicomico) formation are clay, sand, gravel, and ice-borne boulders. As explained above, these materials do not lie in well-defined beds but grade into one another both vertically and horizontally. The coarser deposits have in the main a cross-bedded structure, but the clay and the finer materials are either deposited in lenses or are horizontally stratified. The erratic ice-borne blocks, some of them several feet in diameter, are scattered through the formation and may occur in the gravel, the sand, or the loam. Throughout the formation the coarser material tends to occupy the lower portions and the finer the upper portions, but the transition from one to the other is not marked by an abrupt change, and at many places the coarse materials are in the surface loam and the finer materials are beneath, in the gravel. The coarser beds at the base near Betterton are shown in Plate VII. In the southwest corner of the quadrangle, in the vicinity of St. Margarets, large quantities of Eocene materials have been redeposited in the Wicomico formation. At some places the materials are very much decayed.

The Folio later states:

Thickness. The thickness of the formation is not at all uniform, owing to the uneven surface upon which it was deposited. It ranges from a few feet to 70 feet or more. The greatest thickness in the quadrangle is in the Sassafras River bluffs, west of Betterton, where the formation is at least 70 feet thick. At this place the formation extends to sea level, a condition not observed elsewhere in the quadrangle. (See PL VII.) The formation dips into the valleys and rises on the divides, so that its thickness is not so great as might be supposed from the fact that the base is in many places as low as 40 feet and the top lies in places 100 feet above sea level. Notwithstanding these irregularities, the formation as a whole occupies an approximately horizontal position and has a slight southeasterly dip. Its average thickness in the quadrangle is about 20 feet.

The Folio also states:

Although the formations of the Coastal Plain in the quadrangle are composed almost entirely of unconsolidated materials, yet beds locally indurated are not uncommon and, in the absence of any better stone, furnish considerable material for the construction of foundations and walls. The best stone of this class is the firmly cemented white sandstone in the Raritan formation at White Rocks, in Patapsco River. The gravel beds of the Brandywine formation and the Columbia group are in many places so firmly cemented by iron oxide as to form pebble conglomerates of considerable strength, which have been used locally for foundations. (See PL VII.)