Practice 5The Grand Canyon　　A famous American John Muir said in 1898: “The Grand Canyon…as unearthly in the color and grandeur and quantity of its architecture as if you had found it after death on some other star.”　　Like Muir, those of us who stand along the rim are prompted to wonder about the unearthliness and the forces that created and are still changing this place.　　After more than 100 years of studies, many things are still obscure. Today visitors come by the thousands—the great and simple of the earth — all in a spirit of marvel. Travelers come from every state of the Union, from every country in Europe and Asia, pilgrims to a shrine that is the same as the creed.　　From the depths of the canyon comes welling silence. Seldom can you hear the roar of the river. For all sounds are swallowed in this gulf of space. ‘It makes one want to murmur.  A woman once whispered to her companion. This silence is not the silence of death；rather, it is a presence. It is like a great piece of music. But music made of man works up to a climax and ceases；the Grand Canyon is all climax, a chord echoing into eternity.  Perhaps the most spectacular feature of the Grand Canyon, its Redwall limestone cliff, stands about half way up the chasm and is practically vertical. Its average height is550 feet almost exactly that of the Washington Monument. Though it is actually gray-blue limestone, the surface of the cliff has been stained to a sunset hue by iron salts washing out of the rocks. Above the Redwall come alternating layers of red sandstone and shale(页岩)1, 000 feet thick, then comes the next pale-blue layer. The topmost layers are a yellowish limestone.　　Now, visitors to the South Rim alone may number 18, 000 in a single day. Some of that number will travel by mule(轻型牵引机)train down Bright Angel Trail to the canyon’s floor, cross the raging fiver by a suspension bridge and amount to the North Rim.　　Though the two rims face each other across only 12 miles, it is a journey of 214 miles by car from one to the other. Nor can you visit the North Rim except in summer；some 1, 200 feet higher than the South Rim, it is snow covered much of the year except in July and August.　　But there is no day that you may not visit the South Rim and find the sun warm on your face and the air perfumed with the incense of smoke from an Indian hearth. The Grand Canyon is an unearthly sight. No wonder an American writer and journalist said, “I came here an atheist, and departed a devout believer.”