If you wade out in to the bay, and look back at the cliffs from a distance, you can clearly see several distinct layers. It may be hard to see, but most of these layers slowly dip down as you go further south. So as you go south, the deposits at a certain level get younger. Except for the very top, which contains more recent material, this trend is true along the entire length of the Calvert Cliffs. So Brownie's Beach at the northern most tip is also the oldest part of Calvert Cliffs. The oysterbed, Shattuck's zone 4, is an exception to this trend.
The deposits at B.B. are part of the Calvert Formation which, as the time table below shows, was formed in the early-middle age of the Miocene epoch of the Tertiary period of the Cenozoic era of the Phanerozoic eon. Pffft. The total thickness of the Calvert formation is about 60 meters, but part of that is already below ground/water level at B.B.
A kilometer south of Governor's Run, the Calvert Formation disappears completely below beach level. On top of the Calvert Formation lies the 15-30 meters thick Choptank formation, which in turn disappears below ground level near Calvert Cliffs State Park. And on top of the Choptank formation lies the St. Mary's formation. This trend is very clear in the geologic map of Calvert County at the Maryland Geological Survey.
Within each formation, you can identify distinct layers, from fine blue clays, to coarse red sands. These are called Members. Different members were deposited under different circumstances, from shallow seas to tidal flats, and contain different types of fossils.
| EON | ERA | PERIOD | EPOCH | AGE | FORMATION (in Maryland) |
TIME |
| P h a n e r o z o i c |
Cenozoic | Quaternary | Holocene | 0-10000yr | ||
| Pleistocene | 10000yr-1.6Myr | |||||
| Tertiary* | Pliocene | 1.65-5.2Myr | ||||
| Miocene | late | Eastover | 5.2-25.2Myr | |||
| St. Mary's | ||||||
| middle | Choptank | |||||
| Calvert | ||||||
| early | ||||||
| Old Church | ||||||
| Oligocene | 25.2-36Myr | |||||
| Eocene | 36-54Myr | |||||
| Paleocene | 54-66.5Myr | |||||
| Mesozoic | Cretaceous | 66.5-144Myr | ||||
| Jurassic | 144-213Myr | |||||
| Triassic | 213-248Myr | |||||
| Paleozoic | Permian | 248-286Myr | ||||
| Carboniferous | Pennsylvanian | 286-360Myr | ||||
| Mississippian | ||||||
| Devonian | 360-408Myr | |||||
| Silurian | 408-438Myr | |||||
| Ordovician | 438-505Myr | |||||
| Cambrian | 505-544Myr | |||||
| P r o t e r o z o i c |
Late | 544-1000Myr | ||||
| Middle | 1000-1600Myr | |||||
| Early | 1600-2500Myr | |||||
| A r c h e a n |
Late | 2500-2900Myr | ||||
| Middle | 2900-3400Myr | |||||
| Early | 3400-3900Myr |
Much more recently, streams and rivers have cut down through the many layers and created gaps in the cliffs. These gaps form the present-day beaches, such as B.B. Because of the impermeable clays, several of these gaps are filled with swamps thriving with turtles, water snakes and even a beaver lodge. A walk through Calvert Cliffs State Park is definitely worth it!
 turtle |
 beaver lodge |
 black snake |