In fact, if anything, we probably have too many layers of silt, in my opinion. Why do I say that? The sediment cores – tubes driven into the mud through the layers and extracted, split and analyzed – revealed a 200 year old artifact as much as 9 ft. deep in the mud, just above a hard layer – likely the ‘original bottom of the river’ back in the early 1600s. Think about that- the end of the old dock has seen enough soil deposited here that washed off of farms and construction sites upstream to fill up 9-feet of the depth across a mile wide area in the James in less than two centuries. Much more of that and we won’t have much of a river.
For example, the 9 ft. of sediment at the end of one old dock in 7-8 ft. of water informs us that the water depth at the time of the Revolution was 16-17 ft., which is more than enough for ocean-going vessels carrying heavy loads of tobacco hogsheads. The layers of sediment vary in density with lighter clays and silts interspersed with heavier sandy strata. This is evidence of periodic episodes of calmer weather and then storms/floods that increase currents, suspend and move the lighter soil particles and deposit mostly just the heavier sand. (More research is planned on tying sandy layers to large storm events and other ‘episodic phenomena’).
Larger sand layers may indicate larger floods, such as the historic floods recorded and documented by newspapers and diaries of the past centuries. Add in a few artifacts found in the layers – especially a few that can be dated – and we are well on the way to dating our strata. We might even see historic events like the Great Flood of 1771, the Great Depression or the early 19th century advent of Steamboat passenger service on the river in the sediment’s layers.
The 1771 flood was massive and should have left a large sand or disturbed layer – we will be looking for it in the layers from the sediment cores. The Great Depression saw the decline of farming (after an agricultural boom running from World War I and the mobilization of farmers to help feed war-torn countries), the Civilian Conservation Corps and many public works projects such as planting broad forests on eroding lands. During the 1930’s and the run up to World War II, tens of millions of acres of trees were planted and government agencies were set up to provide soil conservation & erosion prevention services to farmers. The result was that a lot less soil ran off the land in the rain and wind, and the silt layers in the layers at the end of the dock should be thinner.
Sediment chemistry – what the sediment is made of – can reveal quite a lot of data. Artifacts are wonderful if we are lucky enough to catch one in a 4'-inch tube by accident but we can’t count on that too often, despite there being a ‘halo’ of artifacts suspended in the mud around the old dock sites. What we can count on is pollution and several different types of pollution over the ages.
Steamboat service started on the James from Norfolk to Richmond in 1815. We should see a layer of cinders, ash and coal in the sediment layer of that era as it was not uncommon to discard ash from the boilers to the river. The sediment layer of 1825 and later eras, should all have higher levels of ash, coal, clinker and cinders. The Allied Chemical plant in Hopewell got started in 1917 producing 'gun cotton', an explosive considered safer than gunpowder for artillery shells. Other plants producing a variety of products, using chemical feed-stocks and outputting various by-products and wastes, which leave chemical traces in the river sediment. If we know the date an industrial plant started producing a particular product and the chemical fingerprint of the plant’s output, then analysis of the layer of mud from that era should reveal levels of the chemical signature. For establishing the date of a stratum, chemical fingerprints could be as helpful as a dated artifact.
More will be revealed with further cores and other analyses.
Where are we now and where do we go from here?
We’ve undertaken several approaches to explore the potential of the riverfront and river bottom in front of Shirley:
Shoreline surface survey of artifacts in a "catch and release" program with volunteers. This will continue and the data is being analyzed to determine how the concentrations of different artifact types and epochs relate to the features – wharves, docks, landings – on the waterfront and even up the river bank in terrestrial archaeology sites.
Mapping of visible features such as pilings and rock piles by sub-meter GPS and total station. GPS and total station mapping indicates that there 5 wharf sites where once was thought to be one or two of the “old wharves”. Figuring out the succession of wharves – which came first and which one next and so on – and dates for each will be a focus going forward.
Side Scan Sonar and Dual Frequency Sonar Surveys are being conducted. Initial Side Scan Sonar indicated perhaps two sunken vessels poking up out of the mud and a possible 18th century dock site and remnant stone bulkhead along with possible ballast piles (ballast stones were placed in vessels for balance but were often discarded when loading heavy cargos or dragging a vessel on or near shore for repairs). As pilings rot down to the muddy bottom over time, the older groups of pilings are the shortest often. Since the siltation rate is high, it’s likely the tops of the colonial pilings are rotted down and covered by silt. There may be a few exceptional pilings that do not rot at the same rate and can be seen by Sonar. Dual Frequency or Sub Bottom Profiling (marine version of ground penetrating radar) may “see” through the silt and show buried piling tops.
Sediment Cores – initial cores indicate sediment layers and artifacts are present. Future cores are planned when GPS, Sonar and shoreline artifact surveys indicate the most likely sites for the colonial wharves. Also, as the docks were used, artifacts accumulated in the sediment layers around the docks during the period of use. In theory, there should be a “halo'” of artifacts suspended in the mud around a dock. The artifacts should be present in the layers created when the dock was in use.
Geomorphology and Sediment Chemistry – where did the silt come from in each layer? The plow shows up in Virginia about 1650 and marches steadily West with the frontier. Settlers’ plowing and land clearing increases sediment run-off and changes the plant species on the land. The soils erode and the plant pollen blows into the river. Changes in the type & source of sediment and the mix of pollen grains in the layers – as well as the thickness of the layers – should indicate the impacts of land conversion upon the river. Man-made chemicals – coal ash & ‘signature pollution’ from industrial sources– can provide information on dating and potentially, the health of the river.
Dendrochronology of pilings – “Dendro” or tree-ring dating can be used on the pilings to determine a fairly precise date on the construction and repair of a given dock. Once other data has indicated the most likely candidates for the colonial docks, Dendro can help confirm and refine the dates of creation and, possibly, use.
Terrestrial artifact survey & topography – should tie shoreline artifact concentrations to upland terrain features and terrestrial archaeology sites as well as the approaches to the wharves. In other words, if there is not a wharf where there’s a high concentration of artifacts on the shore, there may be an unknown historic site up the bank there. We need to tie the shoreline artifact concentrations to archaeology sites, whether from docks or land-based sites with debris scattering down to the shore.
Historic Records – while they’ve been searched and researched, it’s hard to say we have everything when it’s a known unknown.
We’ve just barely scratched the surface. There is so much to do and that can be discovered. Part of the fun is figuring out the next steps and how to take them. There have only been a few similar projects, five to be exact, and the archaeological methodology is still in the experimental phase – how best to reveal the colonial riverscape hiding under a blanket of silt off the front door. We are very nearly pioneers in a heretofore unexplored world.