Farther down the coast is Charlotte Harbor, also deeply indented and sheltered from the sea by various outlying islands. It is eight to ten miles long and extends twenty-five miles into the land, having valuable oyster-beds and fisheries, and its port is Punta Gorda. Below this is the projecting shore of Punta Rassa, where the outlet of Lake Okeechobee, the Caloosahatchie River, flows to the sea, having the military post of Fort Myers, another popular resort, a short distance inland, upon its bank. The Gulf Coast now trends to the southeast, with various bays, in one of which, with Cape Romano as the guarding headland, is the archipelago of "the ten thousand islands," while below is Cape Sable, the southwestern extremity of Florida. To the southward, distant from the shore, are the long line of Florida Keys, the name coming from the Spanish word _cayo_, an island. This remarkable coral formation marks the northern limit of the Gulf Stream, where it flows swiftly out to round the extremity of the Peninsula and begin its northern course through the Atlantic Ocean. Although well lighted and charted, the Straits of Florida along these reefs are dangerous to navigate and need special pilots. Nowhere rising more than eight to twelve feet above the sea, the Keys thus low-lying are luxuriantly covered with tropical vegetation. From the Dry Tortugas at the west, around to Sand's Key at the entrance to Biscayne Bay, off the Atlantic Coast, about two hundred miles, is a continuous reef of coral, upon the whole extent of which the little builder is still industriously working. The reef is occasionally broken by channels of varying depth, and within the outer line are many habitable islands. The whole space inside this reef is slowly filling up, just as all the Keys are also slowly growing through accretions from floating substances becoming entangled in the myriad roots of the mangroves. The present Florida Reef is a good example of the way in which a large part of the Peninsula was formed. No less than seven old coral reefs have been found to exist south of Lake Okeechobee, and the present one at the very edge of the deep water of the Gulf Stream is probably the last that can be formed, as the little coral-builder cannot live at a greater depth than sixty feet. The Gulf Stream current is so swift and deep along the outer reef that there is no longer a foundation on which to build.