McuEE] TIDES AND CURRENTS 47 



is a[)i)roxiiuately doubled at neap tide and tripled at spring tide twice 

 in each twenty four hours. Then, as the crest of the main debacle 

 advances into the upper gulf beyond Punta Tepopa, the trough of the 

 ebb is already approaching the Tiburon-San Francisqnito constriction; 

 and even bePTC the final flooding of El Infleniillo from the north is 

 completed, the waters of Bahia Kunkaak are receding and a tiderip is 

 tearing through Boca Infieruo at a rate sufficient to half empty the 

 reservoir of its accumulated volume before the ebb trough has rounded 

 the island to the head of the strait. Thus the effect of the exceptional 

 tides of the gulf and the peculiar configuration of Seriland is to concen- 

 trate and accentuate tidal currents in El Iiifiernillo, and to convert the 

 channel into a raceway for nearly continuous tide rips. According 

 to Dewey, the spring tides are 10 feet and the neaps 7 feet about the 

 northern end of the strait;' in December, 1895, the tides about Punta 

 Blanca and Punta (iranita were roughly determined as 13 or 14 feet at 

 spring and 7 or 8 at neap, the range varying considerably with the 

 direction and force of the wind; and the consequent current through 

 Boca Infieruo was estimated at 4 to 8 miles per hour, the higher velocity 

 of course coinciding with the spring tide. The change in direction of 

 the current is almost instantaneous — indeed, the run is in opposite 

 directions on opposite sides of the narrow strait when the wind sets 

 oblicjnely — so that the tidal flow is practically continuous. The cur- 

 rents are of course slacker in the body of the strait, but even here suffice 

 to transport coarse sediments; and it is to this agency that the "shoals 

 and sand spits" noted by Dewey- and the maintenance of a deep 

 channel through Boca lufierno are chiefly to be ascribed. The mate- 

 rials of Punta Tormenta and Punta Tortuga attest the transportation 

 of pebbles up to .3 or 4 inches in diameter by the combined work of 

 waves and tidal currents. 



Like other mountain-bound water bodies, the portion of the gulf 

 washing Seriland is excei>tionally disturbed by winds of given velocity 

 by leason of the high angle of incidence; and moreover the excepticm- 

 ally prominent local configuration disturbs the atmospheric currents in 

 a manner somewhat analogous to that in which the tidal currents are 

 disturbed; so that tlie winds ai-e highly variable but generally strong. 

 Under the combined action of tide and wind the waters are normally 

 ruffied; choppy seas freely flecked with whitecaps are rather the rule 

 than the exception,^ and are rejjlaced less frequently by calms than by 

 steadier billows breaking in continuous surf on sand-beaches (figure 5) 

 and dashing into foam-flecked and rainbow-tinted spray-jets, bathing 

 the rockj' cliffs for 50 feet above their bases. Sometimes the wind stills 

 suddenly, when the sea sinks to rythnnc swells, soon extinguished by 

 reaction from the irregular shores and by the interference of tide-cur- 

 rents; but the swell seldom dies away before the gale springs again. 



' Publication No. 56, U. S. Hydrographic Office, Bureau of Navigation, 1880, p. 142. 



''Op. cit., p. 143. 



■* A stiller and navigable condition of tlie .spa i.s shown in the yiew of Punta Yyuacio, plate iv. 



