2 PEOCEEDINGS OF THE NATIONAL MUSEUM vol. 8a 



Excellent work has been done by Thomas Scott upon the Firth of 

 Forth and by Giesbrecht on the Kieler Foehrde. But even these^ 

 while subject to vigorous tidal fluctuations, do not receive a suf- 

 ficient influx of fresh water to modify sensibly their salinity and 

 temperature. The rivers entering them are few and comparatively 

 small, and the volume of water that they contribute is absorbed and 

 neutralized almost immediately. 



PKCULIAE CONDITIONS OF CHESAPEIAKE BAY 



Chesapeake Bay differs from all that have been mentioned and 

 from most other bays in the world in several particulars, which 

 become of vital importance when considering its plankton. 



Size. — Chesapeake Bay extends almost exactly north and south 

 and in length covers 2%° of latitude, or approximately 200 miles. 

 Its width varies from a few miles near the upper end to 30 miles or 

 more near the mouth of the Potomac River. 



Depth. — Chesapeake Bay, according to geologists, is a submerged 

 river mouth; that is, all the rivers of eastern Virginia and inner 

 Maryland formerly united in a common trunk river which flowed 

 across the present coastal plain and a part of what is now the conti- 

 nental shelf. During the subsequent depression of the Atlantic coast 

 the lower valleys of this river system were submerged to form Chesa- 

 peake Bay. Hence it is comparatively shallow over the greater por- 

 tion of its area, from 10 to 20 meters deep. At only four localities 

 did the depth exceed 30 meters, and at only four others did it fall 

 below 10 meters. Notwithstanding its great size, therefore, it be- 

 comes quite susceptible to the influx of fresh water by reason of its 

 shallowness. 



Tributaries. — Six large rivers flow into the bay, one at the extreme 

 upper end, the others along the western shore. These include three 

 of the longest rivers east of the Alleghenies — the Susquehanna, the 

 Potomac, and the James. The other three, the Patuxent, the Rap- 

 pahannock, and the York, are shorter. Among the small rivers may 

 be mentioned the Patapsco and the Gunpowder, entering the bay 

 from the west, and the Elk, the Chester, the Choptank, the Nanti- 

 coke, the Wicomico, and the Pocomoke from the east. In addition 

 to these are a multitude of tiny rivers, streams, creeks, and runs, all 

 of which contribute to increase the quantity of fresh water poured 

 into the bay. The combined result is a volume amply sufficient to 

 modify materially the water of the bay, and to transform it into 

 an ever-changing mixture of salt and fresh water. 



Salinity. — Since fresh water is lighter than salt water, it has a 

 tendency to remain near the surface, while the heavier salt water stays 

 near the bottom. There are thus produced remarkable differences in 



