Description of provinces.—The continental shelf of the Gulf of Mexico extends from the shore line of parts of the United States and of Mexico outward into the Gulf of Mexico to the abrupt change in bottom slope which is the boundary between this shelf and the continental slope. This change takes place at depths of water in some places as shallow as 400 feet, elsewhere as deep as 700 feet, but a sufficiently good approximation as to the outer edge of the shelf is the 200-meter (656 feet) depth contour which is depicted on the American Geographical Society's Map of the Americas, sheets 1A (1944) and 1-E (1948).

The area of the continental shelf thus defined is 235,000 square miles, and to June 1, 1950, 165 wells have been drilled, distributed as follows.

The shelf adjoins the following political subdivisions.

General geology.—Obviously, with so few wells drilled within the continental shelf of the Gulf of Mexico, it is difficult to present any detailed data from drilling within it. There are, however, some extrapolations from the results of drilling on adjacent land areas, with their geophysical surveys, and from a very limited amount of available geophysical mapping within the continental shelf area which are significant. These data are incorporated in the following discussion.

The Gulf of Mexico is constricted on the east by two peninsulas: the Florida Peninsula and the Yucatan Peninsula. Between these two peninsulas, the Gulf is bounded by a roughly circular coast line. On land adjacent to this