"The Cliffs"

Shattuck's zones

If you have read any books or old publications about the Calvert Cliffs, you probably saw references to Shattuck's zones. Around 1900, George Burbank Shattuck (Amherst College Class of 1892) worked with the Maryland Geological Survey, and published the first comprehensive studies of the stratigraphy of the Chesapeake Bay area. Today, his zones are still in use, although they do not correspond to proper stratigraphic zones. 
What follows is a transcript of parts of Shattuck's description of the zones from the Calvert County volume of the Maryland Geological Survey. It is interesting to compare his descriptions with what you actually can see at Brownie's Beach today. I only include the section on Shattuck's original Calvert formation. The zones continue through the Choptank (16-20) which overlies the Calvert formation unconformably, and the St. Mary's formation (21-24). 
More recently, several of Shattuck's zones have been reassigned. Zone 16 has moved from the Choptank to the Calvert formation, and zone 20 has moved from the Choptank to the St. Mary's formation. 
Shattuck divided the Calvert formation in two members, the Fairhaven diatomaceous earth and the Plum Point marls, not to be confused with the more recent "members" described in the next section. 

[...] The Fairhaven diatomaceous earth has been subdivided into three zones, which may be characterized as follows:

• Zone 1. - At the base of the Calvert formation and lying uncomformably on the Eocene deposits is a bed of brownish sand carrying Phacoides (Lucinoma) contractus. This stratum varies somewhat in thickness from place to place, but does not depart widely from six feet on the average. 

• Zone 2. - Lying immediately above Zone 1 is a thin stratum of white sand of about one foot in thickness, which is locally indurated to form sandstone. It contains a large number of fossils, of which the following are the most important: Ecphora tricostata, Panopea whitfieldi, P. americana, Corbula elevata, Phacoides (Lucinoma) contractus, Venericardia granulata, Astarte cuneiformis, A. thomasi, Thracia conradi, Pecten madisonius, P. humphreysii, Chione latilirata, Cytherea staminea. 

• Zone 3. - This stratum when freshly exposed consists of a greenish colored diatomaceous earth which, on weathering, bleaches to a white or buff-colored deposit breaking with a columnar parting and presenting perpendicular surfaces. It is very rich in diatomaceous matter, the mechanical analyses of specimens yielding more than 50 per cent of diatoms. The thickness of this bed varies from place to place, but where it is penetrated at Chesapeake Beach by an artesian well it has a thickness of about 55 feet. At Fairhaven, where it is well exposed, it caries large numbers of Phacoides (Lucinoma) contractus. This zone is best exposed at Popes Creek, Lyons Creek, Fairhaven, and in stream gullies lying along the northern margin of the Miocene beds. 

[...]From a detailed study of the exposures along the Calvert Cliffs, it has been found possible to subdivide Plum Point marls into 12 zones. They are characterized as follows: 

• Zone 4. - At the base of the Plum Point marls and lying conformably on Zone 3, the uppermost member of the Fairhaven diatomaceous earth is a six-inch deposit of greenish sandy clay carrying Ostrea percrassa. This zone first makes its appearance along the Calvert Cliffs at Chesapeake Beach and continues on down the shore for about 2.5 miles, when it can be no longer distinguished. Throughout this distance, the zone does not dip toward the southeast in harmony with the other zones, which are visible above it, but actually appears to rise slightly against the dip until it finally vanishes at the point indicated. The eratic behavior of this zone would seem to indicate a local migration and temporary occupation of this particular area by Ostrea percrassa. This zone corresponds to "Zone a" of Harris (Tertiary Geology of Calvert Cliffs, Maryland. Amer. Jour. Sci., vol. xlv, 1893, pp 21-31). 

• Zone 5. - This zone is developed immediately above Zone 4 and at Chesapeake Beach has a thickness of 7 feet; as it is followed southward, however, along the Calvert Cliffs, it is found to thin rapidly until at a distance of about 2.5 miles south of Chesapeake Beach it has a thickness of only 2 feet and 6 inches. At this point the base actually lies higher than at Chesapeake Beach, although on account of the thinning the top lies lower. From this point southward it dips away in harmony with the dip of the other beds of the Calvert formation. The materials making up this zone consist of a greenish sandy clay, which carries scattered bands of Corbula elevata. 

• Zone 6. - This zone consists of a greenish sandy clay carrying large numbers of Corbula elevata which are distributed thickly throughout the stratum and not separated in scattered bands as in the zones immediately below and above it. At Chesapeake Beach, where this zone is best developed, it attains a thickness of eight feet, but thins rapidly toward the south, like the two preceding zones, until at a point 2.5 miles south of Chesapeake Beach it has diminished to a thickness of two feet. From this place it continues at about the same thickness until it finally disappears beneath the beach at Plum Point. 

• Zone 7. - Lying immediately above the last layer is a layer of greenish sandy clay, resembling very much in appearance Zone 5, and carrying scattered bands of Corbula elevata. 

• Zone 8. - This stratum is lithologically like those immediately preceding, but varies from them in either being devoid of fossils or in carrying only a few poorly preserved fossil casts of a Corbula, which is probably Corbula elevata. It consists of a greenish sandy clay varying from 9 to 15 feet in thickness. It may be best seen along the Calvert Cliffs from Chesapeake Beach to Plum Point. 

• Zone 9. - This zone consists of greenish and greenish blue sandy clay carrying scattered layers of Corbula elevata and varying in thickness from 6 feet at Chesapeake Beach to 2 feet at Plum Point. 

• Zone 10. - On account of its great and varied assemblage of fossils this stratum is the most conspicuous zone in the entire Calvert formation. It consists of a grayish green or a yellow to brown sandy clay varying in thickness from 6 to 9 feet, and is continuously exposed along the Calvert Cliffs from Chesapeake Beach till it drops below tide two or three miles south of Plum Point Wharf. The following is a partial list of the fossils found in this zone: Turritella indentata, Phacoides anodonta, Crassatellites melinus, Astarte cuneiformis, Ostrea sellaeformis, Pecten madisonius, Macrocallista marylandica, Atrina harisii, Arca subrostata, Glycymeris parillis, etc. It corresponds to "Zone b" of Harris.

• Zone 11. - This stratum consists of a greenish blue to a brown sandy clay changing locally to a sand. It thickens somewhat as it passes down the dip from 5 feet where it is exposed in the bluffs at Chesapeake Beach to 13 feet 1.5 miles south of Plum Point Wharf, where it approaches tide level. It is unfossiliferous or carries a few imperfect fossil casts. 

• Zone 12. - When typically developed, this zone consists of a brownish sandy clay, although at times it changes to a bluish color. In many of its exposures only imperfect fossil casts can be distinguished, but in other places it is found to carry Ecphora quadricostata var. umbilicata, Venus mercenaria, Cytherea staminea, etc. It varies in thickness from two to four feet and corresponds to "Zone c" of Harris. 

• Zone 13. - The materials of this zone consist of a bluish sandy clay more or less changed in sections to a yellowish or brownish color. It carries imperfect fossil casts and varies in thickness from 32 feet at Chesapeake Beach to 10 feet at a point one mile south of Parker Creek, thus gradually thinning as it passes down the dip. 

• Zone 14. - The materials which make up this stratum consist of a brownish to yellowish sandy clay abundantly supplied with Isocardia fraterna. It varies in thickness from 2 to 7 feet and corresponds to "Zone d" of Harris. 

• Zone 15. - This zone is the uppermost member of the Calvert formation and consequently has been considerably eroded so that its true thickness is not definitely known. It consists of a yellowish sandy clay grading down locally into yellowish sand in its local portions. At a point one mile south of Plum Point Wharf this zone shows a greater thickness than anywhere else along the Calvert Cliffs; at that place it measures 48.5 feet. Sections north and south of this point have either been in great part replaced by Pleistocene sand or have suffered by the unconformable overlapping of the Choptank formation. 

• Zone 16. - Note: Shattuck placed this zone in the Choptank Formation, but several recent authors have argued that zone 16 is actually the top most layer in the Calvert formation.

Members

More recently, Shattuck's zones have been grouped in to members: 

* This information was compiled by CMMFC member Edwin Huizinga. Thanks Edwin!!!