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silicified, and stand out in relief, while the mass of the rock is composed of sediment with foraminiferal and encrinital débris. The coral-rag forms a reel in some parts of Wiltshire, but it is rarely seen in section; the corals are obtained as stones from the ploughed fields.

"The conversion of a limestone coral reef into Dolomite becomes comparatively easy of belief, since Mr. Sarby has shown that coral (like nacre) has the constitution of aragonite, a much less stable compound than calcareous spar. Pearly shells are never preserved in calcareous rock, unless in a metamorphic condition; and the corals of the oolite formation are usually silicified, like those of Tisbury, in Wiltshire, and Mattheim, in Germany, or replaced by structureless calcite, full of sparry cavities. It is now also well known that the masses of accumulated chalcedony, called Beckite, found in the neighbourhood of Torquay, are Devonian corals, more or less completely replaced by silica; for they are sometimes hollow, and in other instances contain a nucleus of fossil coral."A. C.

Will you allow me to add to the list of aged "Monarchs of the Forest" which appeared in Science Gossip for August? The Dragon tree of Teneriffe is said by some writers to be the most ancient of all known, trees. Humboldt, when he saw it, computed its age at one thousand years, but I have read that the cypress of Soma, in Lombardy, is the oldest tree of which we possess any record; that there is a chronicle extant at Milan which mentions its being, in the time of that unbeliever in omens who fell on the ides of March (Julius Caesar), a full-grown tree—forty-two years before our Saviour came upon this earth.

There is in Japan a camphor tree which the superstitious in Sorrogi declare to have grown up from the staff of Kobodarsi (a rather famed philosopher, who lived in the eighth century), capable of containing fifteen persons in its hollow. But what is this to the coniferous Wellingtonia gigantea of the slopes of Sierra Nevada? The bark of this tree, put in the form of a room, will hold forty persons—not closely packed together, but seated, with a piano for the benefit of the musical as well. This room made of bark was exhibited in London some years ago, when 150 little children were admitted, and the tree from which it was taken is said to have been three thousand years old. Some ninety trees of this kind are found, all within the circuit of a mile, on the slopes of Sierra Nevada, 5,000 feet above the level of the sea, varying in height from 250 to 300 feet, and in thickness, or diameter, from 10 to 20 feet, the bark being from 12 to 15 inches in thickness.

A writer in the Gardeners' Chronicle says (or rather said a few years ago) that this tree only grows ten inches in diameter in a period of twenty years.

Then we have old trees in our own land—the oak the chestnut, and others. Dryden assigns nine centuries to the oak.

Both the Bull oak of Wedgenorth Park and the Courthorpe oak of Colburn are said to be as ancient as the Norman Conquest. We have likewise Gospel oaks—the "Four Evangelists and the Twelve Apostles," so called because portions of the Gospel were formerly read under them on Holy Thursday.

The Bentley oak and the Winfarthing are believed to have been 700 years old when William came over to conquer us; therefore Dryden's allotted period of nine hundred years has been considerably exceeded by them.

There is a famous chestnut tree in Gloucestershire, at Tortworth, which has been standing since the reign of Stephen (1150), and others at Dorking, in Surrey, planted in 1377.

Our yew trees, likewise, are venerable. The Ankerwyke yew, on the banks of the Thames, opposite Runnymead, in Surrey, was an old tree when Magna Charta was signed in 1251; it yet, I believe, flourishes at any rate it was living and in green leaf a few years ago. There is also at Cliefden Woods a very ancient shell, I may call it, of a yew tree, measuring nearly twenty-seven feet in diameter.

Olive trees are deemed old by modern writers; I ought, probably, to say long-lived, for in the environs of Nice there is one considerably over 900 years old; and some authors assert that a few of the trees on Mount Olivet are 2,000 years in age; nay, more, they say that many of them stood there eleven centuries before the Christian era. There is no doubt that olive trees still thrive on the rocky mountains of Palestine, on the very spot called by Hebrew writers "the Mount of Olives," yet I do doubt their being the self-same trees that grew there in our Lord's time.

A gentleman assured me yesterday that a tree in Tasmania, of the gum tree kind, is both the largest and the oldest in the world. Perhaps some of your readers will tell us something of its history.

Infusoria.—The polishing slate of Bilin, in Prussia, forms a series of strata fourteen feet thick, and is entirely composed of the siliceous shields of Infusoria, of such extreme minuteness, that a cubic inch of the stone contains forty-one thousand millions of distinct organisms.—Mantell's Thoughts on Animalcules.