In the first place, then, the testimony of the deep-sea soundings may be summarized in a few words. Thanks chiefly to the expeditions of the British and American gun boats, "Challenger" and "Dolphin" (though Germany also was associated in this scientific exploration) the bed of the whole Atlantic Ocean is now mapped out, with the result that an immense bank or ridge of great elevation is shown to exist in mid-Atlantic. This ridge stretches in a southwesterly direction from about fifty degrees…