Page:Popular Science Monthly Volume 82.djvu/192

188 these monotonous marshlands are great swells of terra-firma, one hundred or more feet in height and a mile or more in diameter. They are seen from a great distance, and strike one at once as being something out of the ordinary, surely formed by no common method of uplift, less yet by circumdenudation. Of these coastal mounds the so-called "Five Islands," lying to the east of Vermilion and Atchafalaya bays are splendid examples. Belle Isle is just to the west of the Atchafalaya River, between Morgan City and the Gulf, Côte Blanche, Grande Côte, Petite Anse and Côte Carline follow to the northwestward in the order named. The first, or Belle Isle, is famous as the fabled residence of Lafitte, the great Gulf pirate, Grande Côte and Petite Anse for their salt mines and Côte Carline for the southern home of Joe Jefferson, the actor. The drill has demonstrated the fact that these rounding hills are the surface indices of salt masses below. Down one, two or three thousand feet drills have penetrated with but little variation of matter and structure, making, as already observed, the salt masses perhaps as deep or deeper (thicker) than they are in horizontal diameter. Just off the mound one may drill two thousand feet and encounter nothing but soft clays and sand of Quaternary or "Recent" age. Below are similar materials belonging to the Miocene Tertiary; there is no salt, sometimes not even salt water. Such strangely local salt lumps naturally have troubled the philosophical geologist not a little. Some have said they must have been formed in the crater of some dying volcano, sea-waters having oozed in and evaporating deposited salt for years and years in a streaming caldron. But alas for this explanation, these salt masses are not simply the residue of evaporated sea water, they are 99 per cent, chloride of sodium and without the admixture of crater debris. They are pure and solid. Again, though careful magnetic surveys have been made about them, they fail to show any of those erratic local variations sure to occur in volcanic regions. Finally there is proof positive they were never deposited in a hole or depression, but on the contrary have even moved upward bodily through hundreds of feet of surrounding deposits! This seems at first absolutely impossible and as certainly absurd. Nevertheless, we can demonstrate the point beyond doubt. Note that we have said that certain of these salt lumps occur some distance from the Gulf coast, up country, so to speak, where the terranes are of Tertiary and Cretaceous age and are more or less consolidated. For example, in north central Louisiana salt comes near the surface of the soil in circular areas. Surrounding these areas are rings of highly tilted Cretaceous deposits, still outside are the lower Tertiaries, 1,000 or 1,200 feet thick. Clearly then these salt punches, so to speak, have pushed themselves from amongst Cretaceous rocks right through the Lower Tertiaries, bending these strata up on all sides of the mass, to a height of 1,000 or 1,200 feet. The case then seems clear that the salt