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Yet there is a great change in the materials of the rocks of the two formations, shewing that while the bottoms of the seas of the one period had been chiefly arenaceous, those of the other were chiefly clayey and limy. And there is an equal difference between the two periods in respect of both botany and zoology.
In some very rare cases, where the seashore is bordered by coral reefs, as it is in parts of southern Florida, and the strand is made up of limestone bits derived from the hard parts which the polyps secrete, small dunes are made of limy material.
I had once heard a lecturer on hygiene and sanitation speak of the limy coat which forms on the inside of our tea-kettles from using "hard" water. He stated that in time we would get that sort of crust inside of us from drinking water which contained mineral matter. I thought how easy it would be for some of it to chip off and slip into the appendix and set up an inflammation.
Exact drawing of the teeth of two persons. Those in the lower picture began to decay over twenty-five years ago and they were then filled so as to remain perfect. It is wise to have the dentist examine the teeth once or twice every year and remove a limy substance called tartar collecting at their base.
Thus in place of limestone, which would otherwise form, we have only a claylike residuum, such as is obtained when we dissolve lime rocks in acids. This process of solution, by which the limy matter deposited on the bottom is taken back into the water, goes on everywhere, but at a rate which increases with the depth.
However that may be, the Sponges soon begin to absorb the silica or lime of the sea-water, and deposit it in needles or fragments in their bed. The deposit goes on until at last an elaborate framework of thorny, or limy, or flinty material is constructed by the one-celled citizens.
The cup-shaped body is now composed of a large number of limy plates, clothed with flesh; the arms are long, tapering, symmetrical, and richly fringed; the stalk advances higher and higher, until the flower-like animal sometimes waves its feathery arms from the top of a flexible pedestal composed of millions of tiny chalk disks.
Did he apply an acid to the limy wall until it opened before him? Who can find the tools of the cunning workman, or the laboratory where his corrodents are composed? Some rods farther south, the shore is covered with smooth stones, and there you may find the Limpet in great numbers. Patella is the Latin name, but children call it Tent-Shell.
I furnish it with a heap of those limy incrustations wherewith certain springs in the neighborhood cover the dead clump of rushes. It is light, full of holes and gives a faint suggestion of a coral reef. Moreover, it is covered with a short, green, velvety moss, a downy sward of infinitesimal pond weed.
After explaining to him the structural possibilities of apoplexy as a legacy, as I have to you in the cases of insanity, I would continue: "Now by virtue of a possible ancestral weakness of your brain arteries this may happen: the arterial walls, because of habitual food in excess, may undergo a fatty, limy degeneration that will make a rupture possible, with death or paralysis of one-half or more of the body as the direct result; or the small arteries may have their walls so thickened as not to permit enough blood to circulate in order duly to nourish parts of the brain they supply; hence softening of the structure and more or less imbecility.