The Echo is three quarters of a mile long. A rise of the water of merely a few feet connects the three rivers. After long and heavy rains, these rivers sometimes rise to a perpendicular height of more than fifty feet; and then they, as well as the cataracts, exhibit a most terrific appearance. The low arch at the entrance of the Echo, can not be passed when there is a rise of water of even two feet. Once or twice parties have been caught on the further side by a sudden rise, and for a time their alarm was great, not knowing that there was an upper cave through which they could pass, that would lead them around the arch to the Great Walk. This upper cave, or passage, is called Purgatory, and is, for a distance of forty feet, so low, that persons have to crawl on their faces, or, as the guides say, _snake it_. We were pleased to learn that this passage would soon be sufficiently enlarged to enable persons to walk through erect. This accomplished, an excursion to Cleveland's Avenue may be made almost entirely by land, at the same time that all apprehensions of being caught beyond Echo will be removed. It is in these rivers, that the extraordinary white eyeless fish are caught--we secured two of them. There is not the slightest indication of an organ similar to an eye, to be discovered. They have been dissected by skillful anatomists, who declare that they are not only without eyes, but also develope other anomalies in their organization, singularly interesting to the naturalist. "The rivers of Mammoth Cave were never crossed till 1840. Great efforts have been made to discover whence they come and whither they go, yet they still remain as much a mystery as ever--without beginning or end; like eternity."
"Darkly thou glidest onward, Thou deep and hidden wave! The laughing sunshine hath not look'd Into thy secret cave.
Thy current makes no music-- A hollow sound we hear; A muffled voice of mystery, And know that thou art near.
No brighter line of verdure Follows thy lonely way No fairy moss, or lily's cup, Is freshened by thy play."
According to the barometrical measurement of Professor Locke, the rivers of the Cave are nearly on a level with Green River; but the report of Mr. Lee, civil engineer, is widely different. He says, "The bottom of the Little Bat Room Pit is one hundred and twenty feet _below_ the bed of Green River. The Bottomless Pit is also deeper than the bed of Green River, and so far as a surveyor's level can be relied on, the same may be said of the Cavern Pit and some others." The rivers of the Cave were unknown at the time of Mr. Lee's visit in 1835, but they are unquestionably _lower_ than the bottom of the pits, and receive the water which flows from them. According to the statement of Lee, the bed of these rivers is lower than the bed of Green River at its junction with the Ohio, taking for granted that the report of the State engineers as to the extent of fall between a point above the Cave and the Ohio, be correct, of which there is no doubt. "It becomes, then," continues Mr. Lee, in reference to the waters of the Cave, "an object of interesting inquiry to determine in what way it is disposed of. If it empties into Green River, the Ohio, or the ocean, it must run a great distance under ground, with a very small descent."