The boundary between sea and land appears to be the natural datura of 

 reference for measuring elevation of land or depth of the sea. This boundary, 

 however, varies continuously because of the astronomical tides and for other 

 reasons. The various factors which cause this variability are discussed with 

 emphasis on the astronomical tides as the most predictable of the phenomena 

 which affect sea-level. 



Several tidal datums of practical importance are described. Sources of 

 detailed information are identified. Difficulties associated with surveys 

 which extend over a wide range of latitude and elevation are discussed. 



Statistical characteristics of the astronomical tides at various U.S. 

 ports are investigated and documented with graphs and tables. The distribu- 

 tion function for astronomical tidal heights is found to be nearly symmetric 

 at many stations. At many other continental tide stations, the astronomical 

 tide remains above mean sea- level (MSL) more than half the time, but departs 

 farther from MSL in a negative rather than in a positive direction. At 

 Honolulu, Hawaii, the predicted tide is below the MSL more than half the time 

 and positive departures are larger than negative departures. 



A technical glossary and supplementary tables are included. (Author) . 



142 HARRISON, W., MALLOY, R. J., RUSNAK, G. A., AND TERASMAE, J. 1965. 

 "Possible Late Pleistocene Uplift Chesapeake Bay Entrance," Journal of 

 Geology . Vol 73, No. 2, pp 201-229. 



Paleontological and lithological studies of engineering borings and bor- 

 ing logs indicate that a buried, subaerial erosion surface of Pliocene (?) - 

 Pleistocene age cuts across clastic sediments of pre-Yorktownian Miocene age 

 in the subsurface and subbottom of the lower Chesapeake Bay area. When the 

 bore -hole data are coupled with the results of subbottom of the lower Chesa- 

 peake Bay area. When the bore -hole data are coupled with the results of sub- 

 bottom echo profiling and piledriving records, it is possible to construct 

 accurate cross sections of the buried Miocene-Pleistocene contact. The cross 

 sections show "lows" in the erosion surface that may be correlated with the 

 buried channels of the Pleistocene Elizabeth, James, York, and Susquehanna 

 river valleys. Probable channel depths below mean low water at control points 

 are: 100 ft (Elizabeth River, beneath Tunnel No. 1), 155 ft (James River, at 

 Hampton Roads Tunnel), 120 ft (York River, at Yorktown) , 158 ft (Susquehanna 

 River, off Cape Charles City), and 160 ft (Susquehanna River, at Fisherman 

 Island, Cape Charles). The channel depths of what is believed to be the 

 buried Susquehanna River Valley are less than expected when placed on a curve 

 showing the expectable gradients of that stream during the time of the most 

 recent, maximum lowering of sea- level (ca. 18,000 years B.P.). The dis- 

 crepancy suggest uplift of that channel of approximately 170 ft in about the 

 last 18,000 years. Pollen analysis and C" dating of peats and shells 

 immediately overlying the Miocene-Pleistocene contact indicate that the peats 

 were deposited in brackish-water marshes or on boreal flood plains, probably 

 only slightly above sea- level, and that they were subsequently submerged and 

 covered by estuarine sediments. The peats date between 10,340 and 

 15,280 years B.P., and occur at depths of 82-89 ft below mean low rise of sea- 

 level on relatively stable coasts, it seems possible that the peats may have 

 been uplifted as much as 160 ft in the last 15,000 years. 



67 



