The largest natural bridge in the world yet discovered is the Nonnezoshi. It is in Nonnezoshiboko Canyon, Utah, not far from the place where the San Juan River enters the Colorado. This mammoth arch is more of a flying b.u.t.tress spanning the canyon than a real bridge. Its height is three hundred and eight feet and its span two hundred and eighty-five feet.

To visit these bridges from the nearest railway station requires stage and horseback riding for upward of one hundred and twenty-five miles.

The latter part of the journey is made over a faint trail through a rugged country; but the scenery amply repays one for the hardships endured.

The climatic changes during the ages have been such that this region is now almost inaccessible on account of the lack of water, except in the early spring when melting snows yield a temporary supply. Even the cattlemen pasturing their herds in that section keep them there but a few weeks during the year, so scarce is both water and vegetation.

In the main, natural bridges are the result of one or another of several causes. A limestone cavern may be partly destroyed by streams of water, leaving a portion of the cavern with its roof still in place; the part of the roof thus remaining becomes the arch of the bridge. A branch of the Southern Railway threads a natural tunnel near Anniston, Ala., and the tunnel is the remnant of an old limestone cavern.

In other cases a natural bridge is formed when bowlders, or a ma.s.s of rock, tumbling into a deep crevice is wedged and held in place. In still other instances a layer of hard or slowly weathering rock may rest upon a layer of rock which weathers rapidly. In such cases, if the rock layers form the face of a cliff, natural bridges, caverns, and overhangs are apt to result.

CHAPTER XVIII

STRANGE ROCK FORMATIONS--TABLE MOUNTAIN OF CALIFORNIA

There are many table mountains in different parts of the world, but the one which I am about to describe is interesting both from geological and financial stand-points. The so-called Table Mountain of California is a ma.s.sive natural railway embankment or colossal Chinese wall, extending through several counties, but best studied in Tuolumne County.

The mountain is forty miles long, from five hundred to eight hundred feet high, and a quarter of a mile wide at the top. For the most part the top is bare of vegetation and quite level, though slanting slightly toward the south. In places at the base of its precipitous sides, and sometimes extending part way up, pine and other trees are found growing.

This gigantic wall, broken through in several places by flowing rivers, is nothing more nor less than a mighty stream of congealed basaltic lava called lat.i.te, which in prehistoric times, rushing down the western flank of the high Sierras, usurped the bed of an ancient river channel, drinking up the waters and piling up its molten ma.s.s bank high.

The bed of the stream being filled with lava, its waters not flowing through the gravel, were forced to find other channels. The action of the elements during subsequent ages has worn away in great part the banks of the pliocene river and eroded in places the solid slate rocks to the depth of two thousand feet, leaving this sinuous wall as a mute witness of the mighty forces of nature.

On account of the excessive hardness and durability of this kind of basalt, this monumental fortress will endure long after the corroding tooth of time shall have crumbled to dust the royal pyramids and their very memory shall have been lost in oblivion.

Some geologists think there were two volcanic streams of lava, one succeeding the other by an interval of thousands of years, the first covering the auriferous gravel and the second quenching the waters of a subsequent river which had forced a pa.s.sageway through the first flow of lava.

Scores of tunnels have been run into the mountain to get at the gravel of this Pactolian river. Millions of dollars of gold have been extracted from its bed, and millions more await the tunnel, upraise, and drift of the adventurous miner.

Beginning at the top of the mountain and working downward, we find the order of materials as follows: A cap of basalt from sixty to three hundred feet thick, a bed of breccia of varying thickness, two hundred feet of conglomerate andesitic sand (volcanic ash of the miners), a bed of pipe-clay, and then auriferous gravel resting on a bedrock of slate.

In tapping the ancient river-bed considerable water is encountered flowing through the gravel. To get rid of this water has been a problem of expense and annoyance to the miner.

To measure the time that has pa.s.sed since this buried river rolled over golden sands staggers the intellect. It is estimated that from one hundred and fifty thousand to four hundred thousand years must have elapsed.

This curiously formed mountain has been likened to a monolithian serpent. Where the Stanislaus River breaks abruptly through the mountain the eye gazes in wonder from the crest down two thousand feet to a seemingly tiny crowded stream below, rushing madly on its way to the sea.

Many interesting remains of animals have been found in the gravels under this mountain. In running a tunnel under Table Mountain some years ago, the miners came across a large ma.s.s of tallow weighing about one hundred and fifty pounds, and in proximity were the bones and tusks of a huge animal. Many bones and tusks of the mammoth and mastodon, not to mention the remains of other animals, have been found in the ancient river-bed.

Probably some of these elephantine animals were sporting in the water and dashing it over themselves when the stream of lava, sweeping down, overwhelmed them, trying out the tallow and preserving their skeletons for the wonderment of civilized man.

At one place in the mountain the deep roar of a waterfall is heard. At another, where there is a deep break, is a series of pa.s.sageways and caves where the outlaw Murietta had his hiding-place. In several places on the top of the mountain, by striking the foot down hard, a hollow, reverberating sound is heard. We give in his own words the account of an explorer's visit to the so-called Boston tunnel which runs beneath Table Mountain:

"Hearing of a celebrated petrified tree in the Boston tunnel, which runs under Table Mountain, I determined if possible to see it and procure some specimens. After considerable inquiry I found a miner who said he knew where the tree was; that the tunnel in which it was located had been abandoned many years ago; that no persons had entered it for years; that rocks were constantly falling, making it exceedingly dangerous to enter, and that very likely it was so clogged up with rocks that no one could get to the tree. When I had expressed my great desire to see this tree, and coaxed him, at length he promised to take me to the tunnel to see its condition, but said he would not promise to guide me into it.

"Having dressed ourselves in overalls and jumpers, with candles and geological hammers in hand we set out for our destination. On approaching the tunnel my guide at once began to throw stones into the bushes on either side of the entrance. When asked why he threw the stones, he replied that about the mouth of old tunnels rattlesnakes are wont to resort to get out of the burning sun.

"Not finding any rattlers, we proceeded down the incline to the mouth of the tunnel. Finding the mouth not obstructed, and lighting our candles, we entered. Sometimes crawling on our hands and knees over fallen rock with scarcely a foot of extra room above our heads, then stooping low, then walking upright, again crawling between huge ma.s.ses of rock and earth, and crowding between slanting monoliths, we made our way through the mud and water dripping on us from the roof above.

"When part way in, the guide hesitated and declared that we were taking our lives in our hands if we went farther; that the five-ton rock lying in front of our path had very recently fallen from the roof, probably a week before, possibly a day or only an hour before. Pointing to the roof with his candle he said: 'Do you see that piece of rock partly detached and ready to fall at any moment?'

"Acknowledging the threatening conditions, I urged: 'If not too dangerous, I do wish that we might go on until we find the tree.'

"Said he: 'If you promise not to strike any of these rocks with your hammer, we will venture a little farther.'

"You may be a.s.sured that I not only promised, but obeyed.

"At this juncture, I must confess, a peculiar sensation came over me when I thought of the possibility of being buried alive or crushed to death in this subterranean cavern, yet pride kept me from showing the white feather.

"The guide, going ahead and examining the walls and roof, called back to me in a low voice, saying, 'We are now safer.'

"Having traversed the main tunnel for a distance of upward of eight hundred feet, and carefully avoiding its branches, we finally came to the object of our search. This tree, four feet in diameter, of opalized wood, stands upright on the left side of the tunnel. The lava had burned off the bark and partly carbonized the outside part, and then the whole had subsequently taken the form of opal silica. There is a s.p.a.ce of about four inches between the tree and the surrounding lava.

"By raising the candles above our heads we could look up the body of the tree some thirty feet. When we had broken off some choice specimens from the body of the tree with the hammer we left this subterranean world. On emerging from the tunnel the guide said: 'Thank G.o.d, we again see the sunlight.'

"To which I replied: 'Amen.'"

CHAPTER XIX

STRANGE ROCK FORMATIONS--GIBRALTAR

A huge projecting limestone rock, in form like a reclining lion, guards the entrance to the narrow water pa.s.sage which separates Europe from Africa. This wonderful feature, the Rock of Gibraltar, extends directly southward from the mainland of Spain with which it is connected by a low, sandy isthmus. It is about three miles in length and in breadth varies from one-fourth to three-fourths of a mile. Two depressions divide it into three summits, the highest of which is about fourteen hundred feet.

Let us visit the small city lying at its western base and then carefully examine this leviathan sentinel that seems to stand guard over the narrow strait. The special permission of the military commander to examine it or even to remain in the city must first be obtained; we are especially warned that cameras are forbidden and all negatives will be confiscated.

The north face we find to have an almost perpendicular height of twelve hundred feet; its east and west sides also display tremendous precipices. The south face is much lower and slopes toward the sea.

Fortifications of ma.s.sive walls and the best of modern guns protect the lower parts and also the seaward side of the city.

But what are those holes high up on the faces of the rock? They are portholes cut through the rock from interior chambers out of which cannon can be thrust and discharged at an invading enemy. We are curious to learn more about this interesting place, and on questioning our guide are told many remarkable stories.

The Rock of Gibraltar is honeycombed with caves, pa.s.sageways, and chambers, some of which are natural and others artificial. We enter the largest of these natural caves, St. Michael's, and as we stand in the main hall, a s.p.a.cious chamber two hundred feet in length and seventy feet in height, we are amazed at its beauty and grandeur. Colossal columns of stalact.i.tes seem to support its ornamental roof and all around are fantastic figures--foliage of many forms, beautiful statuettes, pillars, pendants, and shapes of picturesque beauty rivalling those of Mammoth Cave. St. Michael's Cave is eleven hundred feet above sea level and is connected by winding pa.s.sages with four other caves of a similar character.

[Ill.u.s.tration: This strong and impregnable place is the Rock of Gibraltar, and the city nestling at its base, Gibraltar]

To six of the caves distinct names have been given. One of the caves is three hundred feet below sea level. About three miles of pa.s.sageways, exclusive of many storage chambers, have been hewn so as to connect the different caves and natural pa.s.sages, and so large have they been made that a wagon can be drawn through them. Within this rock are stored supplies of ammunition and sufficient provisions to last several years.

In clambering about the rock we find cannon carefully concealed in scores of different places ready for use when needed.

In places the rock is overlaid with thin soil which produces a variety of vegetation. There are gra.s.sy glens, with trees, and luxuriant gardens surrounding pretty English cottages. During the rainy season wild flowers in great profusion spring up in all directions, but in the summer the rock presents a dry, barren aspect.

This strong and impregnable place is the Rock of Gibraltar and the city nestling at its base, Gibraltar. The city has a population of twenty-five thousand, of whom several thousand are soldiers forming the garrison. The garrison with their artillery, two pieces of which weigh one hundred tons each, reinforced with the strongest of fortifications, are thought to be capable of withstanding the combined hosts of Christendom.

Early in the eighth century the Moors, perceiving the strategic importance of the promontory, took possession of it and erected fortifications. During the succeeding nine hundred years the fortress was besieged no less than twelve times, and on several occasions was captured by invaders.