MEASURING DEPTH

A generally overlooked measurement is the leadline soundings recorded by Herrera. The sounding lead is the oldest of sailing aids. A weight attached to a cord, knotted at one-fathom intervals, enables a ship captain to plumb the depth of water under his keel. It is simple and accurate.

In preparing to evaluate the evidence of soundings, we must first consider the accuracy of depths recorded on maps compiled up to four centuries after Ponce's time.

Three natural processes, constantly at work in Florida coastal waters, affect depth. They are sea-level increase, soil deposition and geologic change.

The seas have been rising ever since the last ice age. Dr. William Gaither, dean of marine studies at the University of Delaware, estimates that the sea level presently is rising at the rate of six inches per century.

Offsetting this rather rapid rise in Florida is reef building and sedimentation caused by wave action, mangrove growth and mainland erosion. Sea-level measurements by William Lazarus suggest that shallows behind barrier islands fill a bit faster than the sea rises. However, comparison of old and recent hydrological charts by your author indicates the inlets and channels which must carry away riverine discharge have remained about the same depth over the past few centuries.

Studies by two geologists of the University of Florida disclose that the state is rising, although at a rate too slow to have much effect on sailing conditions over a time span of less than half a millennium. Professors Neil Opdyke and R.C. Linquist estimate the state has risen 164 feet in the last 1 1/2 million years. Florida's limestone base slowly leaches away; and the remaining, lighter, land mass floats higher on the earth's molten core.

Unfortunately we can not project sea-level depths backward to Ponce's time with precision. The natural processes discussed do not proceed at a steady pace. We know, for example, that the weather was colder when the Spanish first landed; and this would have slowed polar melting. Sedimentation has occurred more rapidly in this century as agricultural practices exposed topsoil to erosion. Channel cutting must keep up with heavier run-off from city streets and houses, but dredging creates a variable difficult to measure.

After careful analysis of available evidence, it appears there has been no significant net change in the depth of water encountered by the adelantados

up to the present. The destructive and constructive forces of nature along Florida coasts, by coincidence, have been about equal. Modern hydrological maps by the National Oceanic and Atmospheric Administration should be reasonably accurate also for the sixteenth century -- except, of course, where dredging has occurred.

Another measurement to correlate is the length of a fathom. This ancient gauge of ocean depth originally was the length of rope across the chest between two out-stretched hands. This span is now standardized at exactly six feet. In Ponce's time, however, the measurement varied.

A common Spanish length for the fathom, or "braza" was 65.82 inches -- nearly five and a half feet -- according to the "Handbook for Translators of Spanish Historical Documents" by J. Villasand Haggard. We have not been able to verify the length of Ponce's fathom, nor for Soto's. Thus, we must allow for a possible variation in the amount of six inches per fathom.

The matter of depth is important to our study because the shallow waters of Florida limit access. Ponce was relatively unhindered inasmuch as his ships were caravels well suited to exploration along uncharted coasts. Columbus so preferred the caravel Nina for his voyages that he bought a half-interest in her. Ponce sailed to the New World with Columbus in the Nina.

Caravels were generally of 55 tons drawing not more than six feet. Ponce could go just about anywhere, but consistently demonstrated great care in probing strange seas. We can suppose he chose deep water whenever possible and when venturing into shallow inlets would first send in the long boat with a leadsman.

LANDFALL

Ponce, pursuing a course north-northwest, sounded nine fathoms, one league (2.6 miles) from shore. This unique, hydrological relationship is met near two landmarks: Crescent Beach and Daytona Beach.

Our choice between these two places is influenced by the proximity of St. Augustine to the north. After Ponce's first anchorage in open sea with eight fathoms, he sailed "the same way" north for a day before turning south. His silence about the harbor of St. Augustine makes us doubt that he ever reached or passed it.

A landfall off Crescent Beach would put Ponce on the edge of shallows ranging from St. Augustine to Jacksonville. This would require an