20 POPULAR SCIENCE MONTHLY. 



The Savannah Valley, deeply buried on reaching the present sea- 

 shore, crosses the submarine coastal plains at a depth of sixteen hun- 

 dred and fifty feet lower than the floor of the plateau itself, which is 

 already submerged at that point to nineteen hundred and fifty feet 

 beneath the surface of the sea. The canon becomes still deeper upon 

 nearing the edge of the continental shelf. The Altamaha becomes a 

 canon with a depth of fifty-three hundred feet at the point where 

 the continental shelf is submerged twenty-five hundred feet. Its 

 length is about three hundred miles. It terminates in an embay- 

 ment thirteen thousand five hundred feet below the surface of the 

 sea. Among the Bahama Islands, and between them and Cuba, 

 there are several similar fiords or drowned valleys, reaching to 

 depths of from two thousand to twelve thousand feet or more. The 

 straits of Florida, and the fiords extending from them, have afforded 

 special opportunities for studying the submerged valleys. The shal- 

 lowest parts of the straits of Florida are two thousand and sixty-four 

 feet beneath the surface of the sea. From this col, or divide, the 

 Floridian channel extends for a distance of three hundred and fifty 

 miles to a point where it has a depth of ten thousand three hundred 

 and fourteen feet, upon nearing the floor of the Gulf of Mexico. 

 From the same divide the deep Bahaman valley trends in the oppo- 

 site direction, skirting the northern side of the Bahaman group, and 

 becomes a fiord reaching to a depth of about twelve thousand feet 

 near the edge of the continental shelf. The Abacan channel, cross- 

 ing the Bahama banks, may be followed to a similar depth. (See 

 map, and Figs. 5 and 6, page 21.) 



The valley of the Mississippi (buried to a depth of one thou- 

 sand feet before reaching the present mouth of the river) is well 

 marked across the submerged plateau to near the floor of the 

 Gulf of Mexico. The drowned valleys of many other Southern 

 rivers are similarly traceable to the floor of the Gulf of Mexico. 

 The same is true of the submarine channels dissecting the 

 drowned plateaus of the Honduras and Caribbean Seas, as shown 

 on the map. 



Many of the submerged valleys have tributaries converging from 

 all possible directions, as, for example, those of the Floridian chan- 

 nel. There are also numerous short fiords, tributary to those of 

 greater proportions, but these come from the abrupt margins of the 

 continental shelves or islands, like the amphitheaters indenting the 

 high table-lands. 



Of the numerous submarine valleys discovered, a considerable 

 number is shown upon the map, but only a few are cited in the text ; 

 by far the larger proportion lie along directions transverse to the 

 trend of the coast lines and mountain ranges, and consequently they 



