TRANSACTIONS OP THE SECTIONS. 



163 



valley of the Atrato, 300 miles long and 75 broad, and lying between the Antiochian 

 mountains on the east and the Cordillera of the Andes on the west, rain falls almost 

 daily, which accounts for the immense supply of water in that region. On the Pacific 

 side of the Cordillera there is scarcely any rain for eight months of the year. The 

 greater portion of the rain falling in the Atrato valley is caught above the confluence 

 of the Truando. Fifteen large tributaries and numerous smaller streams fall into the 

 Atrato and contribute to the immense lagoons, which form natural reservoirs and a 

 superabundant store of water throughout the year. There are various cogent reasons 

 for selecting the confluence of the Truando as the best point from whence the passage 

 from the Atrato to the Pacific may be effected. In the first place, there is no point 

 of junction with the Atrato by western tributaries so near the level of high water on 

 the Pacific as that of the Truando. It happens to be 9 ft. above the Pacific at high 

 water, and it is therefore of sufficient elevation to prevent the Pacific at high water 

 from flowing through the proposed cut into the Atrato ; while it is not so high 

 as to cause the current from the Atrato to the Pacific at low water to pass through the 

 cut too rapidly. In fact, the elevation of the Truando confluence just preserves a pre- 

 ponderating balance on the side of the Atrato. The Atrato, at the junction of the 

 Salaqui, is only 1 ft. above the level of the Pacific at high water ; but the dividing 

 ridge is 1063 ft. high and 30 miles wide, according to a survey of that route by Mr. 

 Kennish and Mr. Nelson. Should any of the rivers at the mouth of the Atrato be 

 selected without reference to the height and width of the dividing ridge, it may be 

 observed that the maximum tidal wave in the Pacific being 25 ft. and that on the 

 Atlantic only 2 ft., the Pacific at high tide would flow into the Atlantic with a current 

 equal to a head of ll^ft ; and at low water in the Pacific the Atlantic would flow into 

 it with a similar current. In the inlet of the Gulf of Micuel recently called Darien 

 Harbour, the action of the tide is so strong, that Her British Majesty's steamship ' Virago/ 

 commanded by Capt. Prevost, dragged both anchors ahead, and was only brought up by 

 paying out nearly all her cable. The heights of the tides and the levels of the two oceans 

 have been well established by the recent observations of Col. Tolten in Navy Bay on the 

 Atlantic, and in a deep bend of the Bay of Panama on the Pacific. On the Atlantic a 

 consecutive series of thirty-two observations Were taken in the months of August and 

 September during the season of calms. On the Pacific two sets of observations were 

 made : the first during May and June, when fifty-four consecutive tides were observed 

 in a season of calms ; and the second in November and December, when fifty-two 

 consecutive tides were observed in a season of light winds. The results do not exactly 

 correspond, and are given in the following Table : — 



Pacific. 



May and 

 June 



Nov. and 

 Dec. 



Atlantic. 



Aug. and 

 Sept. 



Greatest rise of tide 



Least 



Average 



Mean tide of Pacific above mean tide of Atlantic , . 

 High spring-tide of Pacific above high spring- 1 



tide of Atlantic / 



Low spring-tide of Pacific below low spring-tide "I 



of Atlantic / 



Mean high-tide of Pacific above mean high-tide "1 



of Atlantic J 



Mean low-tide of Pacific helow mean low-tide of \ 



Atlantic J 



Average rise of spring-tides 



Average rise of neap-tides 



1772 

 7-94 



1208 

 0759 



9-40 

 6-55 

 6-25 



473 



14-08 

 9-60 



21-30 

 9-70 



14-10 

 0-140 



10-12 



9-40 



6-73 



5-26 

 17-30 



12-40 



1-60 

 0-63 

 1 16 



These observations make the mean level of the Pacific from 0-14 to 075 higher 

 than the mean level of the Atlantic ; but this is probably owing only to local circum- 

 stances, and it may be assumed that there is no difference in the mean levels of the 



11* 



