Many rushed so savagely that in their eagerness they were thrust out of water onto the carcass until a whaleman cut short their murderous careers with a blubber-spade thrust or two. All giant fish belonging to the shark family are protected by a horny covering of adamantine shagreen, or placoid plates, which provides a resistant protection against attack. In fact this substance is so hard that, when removed, it often wears down emery wheels. Most of it today is removed by chemical solution which eats away the surrounding tissue only, leaving a very fine grade of exceedingly tough and beautiful leather, far stronger than the best cowhide ever tanned. Added to this, the amazing speed of which a shark is capable for short intervals, estimated by natives of many countries at from 35 to 40 miles an hour, results in a truly formidable antagonist among under-sea denizens.
Geologic ages revealed in deposit beds show that sharks have lived in all parts of the world.
Yet, strange to say, almost nothing is to be discovered in evidence of sharks through past ages except teeth. The beds of the world's oceans are paved with the teeth of these big fish, sloughed off year after year and dropped into the ocean floor, or deposited as their hosts died. Since there is no real bone in a shark, only teeth remain undissolved by time and the sea to show that there were giants in those days too. Many which have been found are now fossils, turned to stone by action, ironic reminders of the existence of the sea's roving terror. Many of the small dogfish sharks, caught by fishermen whose nets they ruin, are subjected to a quick, upward thrust of the hand under the protruding snout, breaking the flat nose, whereupon the fish are released.