By geophysical exploration, we can see that the layers of sedimentary rock underlying the coastal plain tilt steeply downward and pass under the broad continental shelf of the Gulf. Down in the layers deposited in the Jurassic period is a thick salt bed of enormous extent, probably formed when this part of the earth was hot and dry, a place of shrinking seas and encroaching deserts. In Louisiana and Texas, and also, it now appears, out in the Gulf itself, extraordinary features known as salt domes are associated with this deposit. These are fingerlike plugs of salt, usually less than a mile across, pushing up from the deep layer toward the earth’s surface. They have been described by geologists as ‘driven up through 5000 to 15,000 feet of sediments by earth pressures, like nails through a board.’ In the states bordering the Gulf such structures have often been associated with oil. It seems probable that on the continental shelf, also, the salt domes may mark large oil deposits.
In exploring the Gulf for oil, therefore, geologists search for the salt domes where the larger oil fields are likely to lie. They use an instrument known as a magnetometer, which measures the variations in magnetic intensity brought about by the salt domes. Gravity meters also help locate the domes by measuring the variation in gravity near them, the specific gravity of salt being less than that of the surrounding sediments. The actual location and outline of the dome are discovered by seismographic exploration, which traces the inclination of the rock strata by recording the reflection of sound waves produced by dynamite explosions. These methods of exploration have been used on land for some years, but only since about 1945 have they been adapted to use in off-shore Gulf waters. The magnetometer has been so improved that it will map continuously while being towed behind a boat or carried in or suspended from a plane. A gravity meter can now be lowered rapidly to the bottom and readings made by remote control. (Once an operator had to descend with it in a diving bell.) Seismic crews may shoot off their dynamite charges and make continuous recordings while their boats are under way.
Despite all these improvements which allow exploration to proceed rapidly, it is no simple matter to obtain oil from undersea fields. Prospecting must be followed by the leasing of potential oil-producing areas, and then by drilling to see whether oil is actually there. Offshore drilling platforms rest on piles that must be driven as far as 250 feet into the floor of the Gulf to withstand the force of waves, especially during the season for hurricanes. Winds, storm waves, fogs, the corrosive gnawing of sea water upon metal structures—all these are hazards that must be faced and overcome. Yet the technical difficulties of far more extensive offshore operations than any now attempted do not discourage specialists in petroleum engineering.
So our search for mineral wealth often leads us back to the seas of ancient times—to the oil pressed from the bodies of fishes, seaweeds, and other forms of plant and animal life and then stored away in ancient rocks; to the rich brines hidden in subterranean pools where the fossil water of old seas still remains; to the layers of salts that are the mineral substances of those old seas laid down as a covering mantle over the continents. Perhaps in time, as we learn the chemical secrets of the corals and sponges and diatoms, we shall depend less on the stored wealth of prehistoric seas and shall go more and more directly to the ocean and the rocks now forming under its shallow waters.
The Encircling Sea
A sea from which birds travel not within a year, so vast it is and fearful.
TO THE ANCIENT GREEKS the ocean was an endless stream that flowed forever around the border of the world, ceaselessly turning upon itself like a wheel, the end of earth, the beginning of heaven. This ocean was boundless; it was infinite. If a person were to venture far out upon it—were such a course thinkable—he would pass through gathering darkness and obscuring fog and would come at last to a dreadful and chaotic blending of sea and sky, a place where whirlpools and yawning abysses waited to draw the traveler down into a dark world from which there was no return.
These ideas are found, in varying form, in much of the literature of the ten centuries before the Christian era, and in later years they keep recurring even through the greater part of the Middle Ages. To the Greeks the familiar Mediterranean was The Sea. Outside, bathing the periphery of the land world, was Oceanus. Perhaps somewhere in its uttermost expanse was the home of the gods and of departed spirits, the Elysian fields. So we meet the ideas of unattainable continents or of beautiful islands in the distant ocean, confusedly mingled with references to a bottomless gulf at the edge of the world—but always around the disc of the habitable world was the vast ocean, encircling all.
Perhaps some word-of-mouth tales of the mysterious northern world, filtering down by way of the early trade routes for amber and tin, colored the conceptions of the early legends, so that the boundary of the land world came to be pictured as a place of fog and storms and darkness. Homer’s Odyssey described the Cimmerians as dwelling in a distant realm of mist and darkness on the shores of Oceanus, and they told of the shepherds who lived in the land of the long day, where the paths of day and night were close. And again perhaps the early poets and historians derived some of their ideas of the ocean from the Phoenicians, whose craft roamed the shores of Europe, Asia, and Africa in search of gold, silver, gems, spices, and wood for their commerce with kings and emperors. It may well be that these sailor-merchants were the first ever to cross an ocean, but history does not record the fact. For at least 2000 years before Christ—probably longer—the flourishing trade of the Phoenicians was plied along the shores of the Red Sea to Syria, to Somaliland, to Arabia, even to India and perhaps to China. Herodotus wrote that they circumnavigated Africa from east to west about 600 B.C., reaching Egypt via the Straits of the Pillars and the Mediterranean. But the Phoenicians themselves said and wrote little or nothing of their voyagings, keeping their trade routes and the sources of their precious cargoes secret. So there are only the vaguest rumors, sketchily supported by archaeological findings, that the Phoenicians may have launched out into the open Pacific.
Nor are there anything but rumors and highly plausible suppositions that the Phoenicians, on their coastwise journeys along western Europe, may have sailed as far north as the Scandinavian peninsula and the Baltic, source of the precious amber. There are no definite traces of any such visits by them, and of course the Phoenicians have left no written record of any. Of one of their European voyages, however, there is a secondhand account. This was the expedition under Himlico of Carthage, which sailed northward along the European coast about the year 500 B.C. Himlico apparently wrote an account of this voyage, although his manuscript was not preserved. But his descriptions are quoted by the Roman Avienus, writing nearly a thousand years later. According to Avienus, Himlico painted a discouraging picture of the coastwise seas of Europe:
These seas can scarcely be sailed through in four months… no breeze drives the ship forward, so dead is the sluggish wind of this idle sea… There is much seaweed among the waves… the surface of the earth is barely covered by a little water… The monsters of the sea move continually hither and thither, and the wild beasts swim among the sluggish and slowly creeping ships.