In this comparison of the level of the two oceans, the Caribbean Sea is placed in opposition to the Pacific : but in reasoning from existing data and our present knowledge, we must admit that the level of the Caribbean Sea is much higher than that of the Atlantic near the old Continent. The north-eastern and eastern trade-winds force a great volume of water from the North Atlantic into the Caribbean Sea, and this is increased by another large volume of water which is brought to that sea by the Guiana current, and which enters it by the straits between the islands of Martinique and Trinidad. [ATLANTIC OCEAN, in GROG. Div.] Such volumes of water, being arrested by the long isthmus which separates the Caribbean Sea and the Gulf of Mexico from the Pacific, must produce a considerable accnmulation of water along the western shores of those seas, and raise them above the common level of the Atlantic, and this fact is confirmed by the rapid current called the Gulf stream. [Ams.mo Ocitax, in GEoo. Div.] Opinion varies considerably as to the differ ence of level between the Gulf of Mexico and the Atlantic. Poussin found the level of the Gulf at the mouth of the river Suwaneo 3.75 feet higher than that of the Atlantic at the mouth of St. Johu'e River in Florida : but when Darby, iu his' View of the United States,' estimates the difference between the Gulf near the island of Cuba and did entrance of Chesapeake Bay as at least 83 feet, we must suppose that ho has formed his opinion on erroneous data Also, we cannot accede to the opinion of Humboldt, who, in compar ing some barometrical observations made at Cumana, Cartagena, aud Vera Cruz, with others made at Acapulco and Callao, came to the con clusion that in these parts the Pacific was about feet lower than the Caribbean Sea and the Gulf of Mexico. Lloyd found the reverse to be the case at the mouth of the Chagres and at Panama, as we have mentioned above.
Mathematical investigation, founded on modern exact physical research, has however led to the discovery at once of a cause of difference of level in the sea, very different from any of the causes considered above, and of an example of that difference of the most interesting and instructive character. In the Philosophical Transac tions' for 1859, p. 779-796, is a paper by Archdeacon Pratt, On the Influence of the Ocean on the Plumb-line in India,' which is a sequel to two former communications on the effect of Mountain Attraction on the Plumb-line in India. In this paper the author first describes the remarkable nature of the geographical position of Hindustan, con sisting in this :—that the highest mountain-ground in the world lies to the north of it, and an unbroken expanse of ocean extends from its shores down to the neighbourhood of the South Pole. Now as water is lighter than land, that is, the quantity of matter contained in a given bulk of water is less than that contained in an equal bulk of land, the attraction or attractive power of the ocean is smaller than that of the land. A given bulk of land has a greater attractive power than an equal bulk of sea. Therefore, the sea on the shores of Hindustan is more attracted by the land than by the mina of the ocean beyond. The tendency of this. therefore, is to draw up the ways to a higher les el en the northern shores of the peninsula than at its southern extremity at Cape Comorin. But besides this, the mountain limas of Thibet and the Ilimalaya [Nauss] presents a great excess of matter on the north, above that of the land of ordinary height, and conse quently has a more powerful attraction, which Is added to that of the laud of Hindustan gciwrally, lu drawing up the sea to a greater height at the northern extremity f the peninsula than at the southern.
Accordingly, it has been found by Archdeacon Pratt that the elevation of the somievel at Kurachee, on the north side of the Arabian Sea, is 515 feet above that at Cape Comorin, and it must be about the same at the sarallwasla of Calcutta, at the north end of the bay of Bengal. Now the sea is our only standard of measurement to which the form of the earth can be referred. Regarding it as the general surface of the globe, all elevations above or depressions below that surface are, as we have seen, measured from it. But these 500 or 600 feet, fortunately, are the greatest extent to which the sea-level can be affected, as there is no part of the globe where the attraction on one side, and the deficiency of attraction on the other, can be so great as in that 'articular portion of the world where this difference exists.
The bottom of the sea is similar to the surface of the land as to the irregular succession of elevations and depressions, and it is diversified by mountains and valleys and plains of different elevation. The sum mits of the submarine mountains rise above the level of the sea iu the form of islands. in several parts large table-lands are found, whose surface is not at a great depth below the level of the sea : when their surface is covered with sand, they rum named sand-banks; and when it conaists of coral rocks, coral-bauks. Near the edges of these banks the depth of the sea is generally very great. Some of the summits are barren, others are covered with vegetation, but tdl teem with life of one order or other. The most extensive formation of the submarine table-lands occurs in the North Atlantic. its most north-eastern por tion is foruied by the Outer Bank and the Great Bank of Newfound land. [Nr.wrocNotaxn, in Gsou. Div.] West of the Great Bank of Newfoundland are Whale Bank, Green Bank, Banquereau, and Mizen Bank. The three last-mentioned banks are situated in front of the entrance of the Gulf of St. Lawrence. Opposite the coasts of Nova Scotia are Sable Bank and Le Have Bank ; and then follow, in the immune south-western direction, St. George's Bank, or the banks of Nan tucket, which approach the continent of North America in the vicinity of New York. From this point the banks occur at a short distance from the shores of the United States, and extend, almost without interruption, to Cape Florida and Sable Point, the most southern extremity of the peninsula of Florida. West of this peninsula is tho Tortuga Bank, the continuation of which skirts the shores of the United States iu the Gulf of Mexico as far west as the mouths of the Mississippi. This series of banks occupies more than 1400 miles in length ; but there is always water enough on them for the largest vessels, with the exception of the Virgin Rocks on the Great Bank of Newfoundland, and the shoals of St. George's Bank. In all the other parts the least depth is not less than ten fathoms, and in general forty fathoms of water are found on them. The surface of these banks is very level. Along the northern and north-western edge, which lies opposite to the coast of America, the depth suddenly descends to 100 fathoms, and along the southern edge to 300 fathoms. The descent from the edge of the bank to the deep sea is nearly perpendicular. The banks, especially thoso north of N. Lit., are frequented by immense shoals of fish, especially cod.