The fossils are quite distinct from those which are found in the Patapsco formation and abound much more largely in dicotyledonous types of vegetable life. Most of the species are identical with those found in the Amboy clays of New Jersey which form the northern extension of the formation as developed in Maryland.

THE MATAWAN FORMATION.-The Matawan formation receives its name from Matawan creek in Monmouth county, New Jersey, where the deposits of this horizon are typically developed. It is the most widely extended of the upper Cretaceous formations and reaches from the shores of the Raritan Bay across New Jersey, Delaware and Maryland to the Potomac river. Throughout Virginia it is buried beneath later deposits which have transgressed it, but it reappears again in the Carolinas. Within the limits of Maryland it forms a narrow belt which crosses southern Cecil and northern Kent counties, and then reappears upon the western shore of the Chesapeake in eastern Anne Arundel county, and thence continues southwesterly with constantly narrowing confines across Anne Arundel and Prince George's counties, during the latter part of its course appearing as a narrow band along the westward face of an ill-defined escarpment.

The deposits of the Matawan formation consist mainly of dark colored micaceous, sandy clays, which are generally argillaceous in their lower part and sandy toward the top. Upon the eastern shore of Maryland the Matawan formation has a thickness of very nearly 100 feet, but it has already considerably declined in eastern Anne Arundel county, where it is about 50 feet, and thence continues to decrease southeastward, until in the vicinity of Fort Washington it has declined to 15 feet in thickness, as a result of the gradual transgression of the Eocene deposits.

The fossils of the Matawan formation are highly characteristic of its upper Cretaceous age. Numerous marine mollusca, among them several species of characteristic ammonites, are found among its fauna. Some of these forms range into the next succeeding Monmouth formation, but many are restricted to the Matawan.

THE MONMOUTH FORMATION.-The Monmouth formation, called from its typical development in the region of the Monmouth

Battle Ground, in Monmouth county, New Jersey, extends from New Jersey southward across Delaware into Maryland, but is much less extensively or typically developed in the state of Maryland than to the northward, although some of its characteristic features are still prominent. The Monmouth formation lies to the east of the Matawan deposits above described and forms a narrow belt crossing Cecil, Kent, Anne Arundel and portions of Prince George's counties, but gradually disappears beyond the valley of the Patuxent as a result of the transgression of the Eocene deposits.

Upon the eastern shore of Maryland we find the three subdivisions of the Monmouth formation which characterize the New Jersey deposits represented, viz.: the basal red sands (Mount Laurel sands), overlain by a well defined marl bed (Navesink marl), and this in turn capped by slightly glauconitic red sands (Redbank sands); but upon the western shore of Maryland the differentiation of the Monmouth formation into these several parts is no longer possible, the formation being represented by fine pinkish sands, which are sparingly glauconitic and which show no constant separation into lithologic zones. The deposits have a thickness of about 75 feet upon the eastern shore, but do not exceed 50 feet in Anne Arundel county, and gradually decline in thickness until their final disappearance beyond the Patuxent valley.

The fossils of the Monmouth formation are not strikingly different from those of the Matawan formation, although there are many which are distinctive; while at the same time the more characteristic forms of the Matawan formation are not found in the Monmouth. The deposits are of undoubted upper Cretaceous age.

THE RANCOCAS FORMATION.-The Rancocas formation, so called from its typical occurrence in the valley of Rancocas creek in southern New Jersey, is well developed upon the eastern shore of Maryland, where it forms a broad belt across Cecil and Kent counties to the east of the Monmouth formation, and is the direct southward extension of similar deposits in New Jersey and Delaware. On the western side of the Chesapeake Bay it is found in only a few isolated patches in the extreme eastern portion of Anne Arundel county near the mouths of the Severn and Magothy rivers.

MARYLAND GEOLOGICAL SURVEY

195

The Rancocas formation consists of greensand marls, which in some. localities are highly calcareous on account of the large number of shells of various molluscan forms. In general the deposits are quite arenaceous and are commonly less glauconitic than the same beds in New Jersey. The deposits have a thickness of from 50 to 60 feet in Kent county, where they are most extensively developed, but on the western shore of the Chesapeake they nowhere appear at the surface with a greater thickness than 4 or 5 feet.

The fossils of the Rancocas formation are highly characteristic and are in the main quite distinct from those which are found in the Matawan and Monmouth formations. Their upper Cretaceous age is, however, clearly apparent, and they are generally regarded as occupying a very high position in that division.

THE EOCENE PERIOD.

The deposits overlying the Cretaceous formations, above described, have, from a very early period, been regarded as of early Tertiary age, although our knowledge of them was confined to a few localities. from which characteristic fossils had been obtained. Later study, however, has shown both the proper stratigraphic and paleontologic relations of these deposits, so that they are now well understood.

THE PAMUNKEY FORMATION.-The Pamunkey formation, so called from its highly characteristic development in the valley of the Pamunkey river in Virginia, extends across Maryland from northeast to southwest, through the counties of Kent and Queen Anne's on the Eastern Shore and of Anne Arundel, Prince George's and Charles in southern Maryland. Its area of outcrop constantly broadens from the Delaware line (to the north of which it is buried by the transgression of the Neocene deposits) toward the southwest, and in the valley of the Potomac river has a width of more than 15 miles.

The deposits of the Pamunkey formation are highly glauconitic and are found in their unweathered state either as dark gray or green sands or clays. The glauconite varies in amount from very nearly pure beds of that substance to deposits in which the arenaceous and argillaceous elements predominate, although the strata are generally

very homogeneous through considerable thicknesses. In certain horizons the shells of organisms are found commingled with the glauconitic materials in such numbers as largely to make up the beds, producing what is known as a greensand marl, and these beds are at times so indurated as to form limestone layers. When the glauconite is weathered the deposits lose their characteristic gray and green color and generally become lighter gray with reddish or reddish brown streaks or bands, or may become entirely of the latter color. In this condition they are often cemented into a ferruginous sandstone. The unweathered deposits are found mainly in Charles and Prince George's counties, while the weathered beds appear chiefly to the northward in Anne Arundel county and upon the eastern shore of the Chesapeake.

The fossils of the Pamunkey formation are numerous and characteristic and admit of separation into two clearly defined faunal zones, the lower of which has been described as the Aquia Creek stage and the upper as the Woodstock stage.

The Aquia Creek stage, so called from its typical development along the banks of Aquia creek, a tributary of the Potomac, contains a highly characteristic fauna, which has caused the correlation of this division with the lower Eocene of the southern Atlantic and Gulf states. No satisfactory stratigraphic limits have as yet been assigned to this division and the deposits seem to grade gradually upward into the overlying division.

The Woodstock stage, so called from its typical development at Woodstock, Va., on the southern bank of the Potomac, about 15 miles below Aquia creek, is characterized by a fauna which has been shown to be the same as that contained in the middle Eocene in the Gulf states. As above stated, no satisfactory stratigraphic line has as yet been detected separating this division from that which is found beneath it, so that it may be regarded for the present simply as a faunal

zone.

THE NEOCENE PERIOD.

The Neocene deposits of Maryland occupy a broad area in the eastern portion of the state and consist of strata which attain greater thickness than those of any other period represented in the Coastal

Plain, with the possible exception of the Cretaceous.

The deposits of

Neocene age have been divided into two formations, viz., the Chesapeake and Lafayette formations.

THE CHESAPEAKE FORMATION.-The Chesapeake formation, so called from its extensive development upon the shores of the Chesapeake Bay, extends as a broad belt across the state and occurs likewise in the areas both to the north and the south of Maryland as an important member of the Coastal Plain series. The strata overlie unconformably those of the Pamunkey formation and gradually overlap the latter toward the north, and just beyond the Delaware border rest directly upon the upper Cretaceous beds.

The deposits of the Chesapeake formation consist of sands, clays, marls and diatomaceous beds, the latter composed chiefly of the tests of the microscopic plant forms called diatoms, and mainly confined to the lower portion of the formation. The diatomaceous beds afford fine sections at Pope's creek on the Potomac, at the mouth of Lyon's creek, a tributary of the Patuxent, and at Herring Bay on the west shore of the Chesapeake. At these points the light colored bluffs are very striking objects in the landscape. The nearly pure diatomaceous earth reaches a thickness of about 30 feet, although the remains of diatoms are found scattered in greater or less amounts throughout the overlying strata. This diatomaceous earth can be traced from the eastern shore of Maryland entirely across the state and thence southward into Virginia. From its wide occurrence in the vicinity of Richmond it is sometimes known as "Richmond earth." It was long referred to in the literature of the subject as "Bermuda earth," from its supposed occurrence on the Island of Bermuda, but the specimen upon which the reference was based was ultimately shown to have come from "Bermuda Hundred " on the James river. The diatomaceous earth is frequently described under the names of "Infusorial earth," "Tripoli" and "Silica." The higher portions of the Chesapeake formation are comprised of sands and clays of various colors and frequently carry vast numbers of molluscan shells. Extensive beds of shell marl underlie much of the Miocene country. These deposits become at times cemented into hard limestone ledges. At