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Mineralogy and Geology. 433 
2. Petrified Forest near Cairo; (Atheneum, Jan. 1846, p. 130.)— 
The following particulars are from an account given by Dr. Buist, of 
Bombay, in explanation of some specimens of silicified wood presented 
by him to the Literary Society of St. Andrews :—‘* The specimens 
consisted of about forty-five pieces of wood ;—trunks, roots, knots and 
branches, from-three inches to three feet in length; some were exhib- 
ited sliced and transparent, showing the sap vessels and the medullary 
rays ; some cut into bracelets and brooches. In explaining the pecu- 
liarities of these, Dr. Buist stated that few things were more remarka- 
ble—few less noticéd (considering how worthy it was of examination,) 
than the petrified forest near Cairo. From the city you proceeded, by 
the Caliphs’ Tombs, to the southeast. Passing for five miles through 
an arid valley, through which a river torrent appeared to have flowed, 
skirted on both sides by low, brown, rocky ridges, the traveller turns 
suddenly off to the right, and beyond the first range of sand-hills, finds, 
spreading far as the eye can reach, a vast expanse of rolling hillocks, 
covered with prostrate trees. At first sight these wear exactly the as- 
pect of rotten wood dug out from a Scottish or Irish peat-bog. The 
color and the amount of decay seem the same. They are lying in all 
positions and directions on the surface of the burning sand—some forty 
or fifty feet in length, and one or two feet in thickness ; not continuous 
or entire, but in a line broken across, left in their places like sawn 
trunks. On touching them, instead of proving mouldering and decayed, 
they turn out to be hard and sharp as flints. They ring like cast-iron, 
strike fire with steel, and scratch glass. The sap-vessels and medulla- 
ry rays—the very bark and marks of worms and insects, and even the 
‘spiral vessels, remain entire ; the minutest fibres of the vegetable struc- 
ture are discernible by the microscope. Here you have the carbon— 
the most indestructible matter known to us—entirely withdrawn, and 
substituted in its place a mass of silica—a matter insoluble by any or- 
dinary agent, and at any common heat. Yet so tranquilly has the ex- 
change been accomplished, that not one atom has been disturbed ; the 
- finest tissues remain entire—the most delicate arrangements uninterfe- 
red with. The limits of the petrified forest are unknown: it probably 
extends over an area of many hundreds, perhaps thousands of miles. 
It has never been described with any care, and, extraordinary as it is, 
has excited very little attention. The trees are scattered loosely and 
at intervals over the desert all the way from Cairo to Suez, a distance 
of 86 miles. No theory of their silicification or their appearance 
where they are found, has ever been attempted. The late Dr. Mal- 
colmson found fragments of the wood imbedded in the conglomerate 
which contains the Egyptian jaspers, and threw it out as possible that 
they and the gravel of the Desert, consisting almost entirely of jas- 
