404 



A TL A NTIC ES TUA RINE TID ES 



low. This constriction toward its mouth is shared by a number 

 of the tributaries. The result is, in the main bay, a tide rather 

 of the river or sound type. For two-thirds its length the range 

 uniformly diminishes from 2.6 feet at the capes to 0.8 feet near 

 Annapolis, a distance of 120 miles. So in the lower courses of 

 the greater tributaries, the James, the Rappahannock, and the 

 Potomac, ranges decrease or waver, as may be noted in the accom- 

 panying diagram. The rate of high -water advance is also irreg- 

 ular, as appears on the map ; but the upper course of the bay 

 and larger rivers and the whole course of the smaller streams 

 have bay tides as far as ranges are concerned — i. e., the tide range 

 increases upstream. Though this is not accompanied by the pro- 

 gressive retardation of the true 



iSac^afras 



DIAGRAM 



OF RANGES 



CHESAPEAKF TIDES 



Patuxent 



Potor 



Rappahannock 



James 



York 



Chester 



Pocomoke 



bay tide, it makes the Chesa- 

 peake waters present a curious 

 inversion. Ranges of the river 

 type are interposed between bay 

 tides and the ocean. Two-thirds 

 of the Chesapeake is rather river 

 than bay, and two-thirds of the 

 Potomac is rather bay than 

 river. The narrowing and shoal- 

 ing at the bay-mouth, imitated 

 in the tributaries, explains the 

 anomaly. Thus it happens that 

 a range of 2.6 feet at the capes 

 diminishes up the bay, but again 

 increases to 4 feet at Richmond and 3 feet at Washington. The 

 rate of progress of the tide-wave is r hiere, as commonly, 10 to 

 12 miles per hour. AVhen one tide is just above Washington 

 another is entering the bay from the Atlantic, and high water 

 reaches Havre de Grace, on the Susquehanna, as the following 

 high water enters the mouth of the Rappahannock. The wave- 

 front shows the usual steepening with advance. At Richmond 

 the duration of rise is 4 h. 25 m. ; at Fredericksburg, 4 h. 19 mi. ; 

 at Washington, 5 h. 45 m. Port Deposit, on the Susquehanna, 

 has the phenomenon of steeper back than front. A similar 

 aspect is given at Galveston and perhaps at Falmouth by in- 

 terference and a special development of the diurnal wave. 



In every river an ascending wave must finally disappear. Of 

 the Chesapeake rivers only the Elk shows this. The Pocomoke 

 probably does ; but we have no observations above Snow Hill, 



