PLIOCENE

Unconformably above the formations just described, lies the Bryn Mawr formation, the only beds referred to this age in the State.

Very extensive areas of this material are found covering parts of Prince George's County, extending from Washington southeast into Charles County, and in the vicinity of Charlotte Hall. This formation will never be a producer of molding sand because it is too poorly sorted and is composed principally of a fine, silty clay at the surface along the principal transportation routes of Prince George's and Charles Counties, as well as in other places.

PLEISTOCENE

The deposits of this age are usually spoken of as terraces and have been divided into three distinct formations according to their relative elevation above sea level. The highest and oldest is known as the Sunderland, the intermediate one the Wicomico, and the youngest and lowest the Talbot.

The oldest of these, the Sunderland, reaches an elevation of 200-225 feet around Baltimore and Washington, and slopes southeasterly to an elevation of between 50 and 100 feet at the southern end of St. Mary's County. The next youngest terrace, the Wicomico, reaches an elevation of 100 feet and slightly less around Baltimore and Washington and slopes southeasterly to an elevation of less than 50 feet at the southern end of St. Mary's County. The youngest, the Talbot, seems to have rather a constant elevation of about 45 feet in the areas north of Drum Point on Chesapeake Bay and Maryland Point on the Potomac River, but south of these it slopes rather rapidly to an elevation of about 10 feet at the southern tip of St. Mary's County. These deposits are very extensively distributed over the area investigated, especially in the sections along the main bodies of water, such as Chesapeake Bay, the Potomac River and Patuxent River.

The nature of the material contained in these terraces would indicate that they were deposited under rather unstable conditions, both from the point of material supplied and from the condition of the body of

water in which they were laid down. These facts have a bearing on the possibilities of their being molding sand producing formations. The Sunderland, in the northern part of the area, just south of Baltimore, is principally gravel and contains an occasional boulder. This seems to indicate a very near-shore phase of deposition. As this deposit is followed south into the southern part of Anne Arundel County and the northern part of Calvert County, the unstable conditions seem to exist, but the type of material being deposited seems to be somewhat finer, and in places deposits of molding sand have been noted. Any production from this formation in this area, however, will without doubt be irregular and spotted.

The Wicomico, in general, resembles the Sunderland in origin except that the material supplied at this stage seems much finer. Of the three Pleistocene terraces, this one promises to be the most important

FIG. 1.-Profile of Pleistocene terraces showing deposition of molding sand at the inner margin of the Wicomico terrace

as a producer of sand. It is now being worked in one locality in Prince George County and has been prospected in many others.

An interesting relation was noted to exist between the older Sunderland terrace and the Wicomico. This relation, briefly stated, is this: molding sand seems to have formed at the junction of the two terraces, see Figure 1.

This may be accounted for in the following manner: The Sunderland terrace developed and the sea withdrew or the land rose establishing a new plane of erosion and deposition at the level of the Wicomico terrace. After this level was well established, the sea again withdrew at what appears to have been a somewhat slower rate. During the time of the withdrawal of the sea to the Talbot level, the waves and currents had an opportunity to rework the material in the Wicomico terrace and deposit the finer parts of it far back at the base of the Sun

derland terrace at its junction with the Wicomico.

The last part of

This explanation

this process is diagramatically shown in Figure 1. seems to account best for the deposits which have this geological occurrence.

The Talbot, which is the youngest and lowest of the Pleistocene terraces was examined as a source of molding sand, but with no success. This terrace is very gravelly and the sand is mostly sharp sand, poorly sorted, and worthless as a foundry material.

OCCURRENCE AND PROPERTIES OF MOLDING SAND DEPOSITS

INTRODUCTION

The accounts of the molding sand deposits of the state are arranged according to counties and geological formations. The descriptions include the following points: (a) location, geographic and situation. with respect to transportation; (b) the geological formation in which the sand occurs, and the extent of the individual deposit; (c) collection of the samples; (d) owner of the property when determined; (e) use if being worked; and (f) test data.

ANNE ARUNDEL COUNTY

CRETACEOUS

MATAWAN FORMATION.-What appears to be a good deposit of molding sand was found outcropping on the Annapolis road one-quarter mile south of Boon Station. Here the road and tracks of the Baltimore and Annapolis Short Line Railroad run parallel to each other for some distance, never being more than one-eighth of a mile apart. The deposit where sampled showed the following section:

Fine sand and gravel..

Red to brown clayey sand..

2 feet
4 feet exposed

This same type of sand is exposed for about two miles southeast along the road from the point where it was sampled. The upper part of the

section is slightly consolidated but a mixture of the whole gives a sand with an excellent feel.

MOLDING SAND, MILE SOUTH OF BOON STATION

Sample No. 1505 was collected from a road side pit which was opened for road patching material.

The sand gives the following results on test:

Coarseness figure .683, equivalent to 1 Albany sand, Grain fineness 90, Grain class 4, Clay class F, Dye Adsorption figure 1976.

This sand shows excellent bond strength and permeability at 8.1% water content. This percentage of water is near the one at which many sands are worked in the foundry.

Another sample from the same formation was collected near the southern limit of the area mapped as Matawan, at a point 100 yards

south of the crossing at Jones Station on the Baltimore and Annapolis Short Line. Here there are four to five feet of molding sand overlain by a foot and a half to two feet of sandy silt. The topography of the area would indicate that this deposit might have some areal extent.

MOLDING SAND, 100 YARDS SOUTH OF JONES STATION

The sample, No. 1508, was collected from the four foot face exposed at the roadside, and showed the following results on test:

Coarseness figure, .707, equivalent to 1 Albany sand; Grain fineness, 118; Grain class, 3; Clay class E, Dye Adsorption figure 1976.

This sand was tested along with many others for refractoriness during an investigation carried on, on the refractoriness of molding sands. The sands were fired under as near oxidizing conditions as possible at intervals of four Segar cones, starting at cone 4. This sand seems to be very refractory, showing only softening at cone 19, 1510°C. The clay was separated from this sand and also tested by firing. It was