The Little Bat Room Cave--a branch of Audubon Avenue,--is on the left as you advance, and not more than three-hundred yards from the great vestibule. It is but little more than a quarter of a mile in length, and is remarkable for its pit of two-hundred and eighty feet in depth; and as being the hibernal resort of bats. Tens of thousands of them are seen hanging from the walls, in apparently a torpid state, during the winter, but no sooner does the spring open, than they disappear. Returning from the Little Bat Room and Audubon Avenue, we pass again through the vestibule, and enter the Main Cave or Grand Gallery. This is a vast tunnel extending for miles, averaging throughout, fifty feet in width by as many in height It is truly a noble subterranean avenue; the largest of which man has any knowledge, and replete with interest, from its varied characteristics and majestic grandeur. Proceeding down the main Cave about a quarter of a mile, we came to the Kentucky Cliffs, so called from the fancied resemblance to the cliffs on the Kentucky River, and descending gradually about twenty feet entered the church, when our guide was discovered in the _pulpit_ fifteen feet above us, having reached there by a gallery which leads from the cliffs. The ceiling here is sixty three feet high, and the church itself, including the recess, cannot be less than one hundred feet in diameter. Eight or ten feet above and immediately behind the pulpit, is the organ loft, which is sufficiently capacious for an. organ and choir of the largest size. There would appear to be something like design in all this;--here is a church large enough to accomodate thousands, a solid projection of the wall of the Cave to serve as a pulpit, and a few feet back a place for an organ and choir. In this great temple of nature, religious service has been frequently held, and it requires but a slight effort on the part of a speaker, to make himself distinctly heard by the largest congregation. Sometimes the guides climb up the high and ragged sides, and suspend lamps in the crevices and on the projections of the rock, thus lighting up a scene of wild grandeur and sublimity. Concerts too have been held here, and the melody of song has been heard, such as would delight the ear of a Catalini or a Malibran. Leaving the church you will observe, on ascending, a large embankment of lixiviated earth thrown out by the miners more than thirty years ago, the print of wagon wheels and the tracks of oxen, as distinctly defined as though they were made but yesterday; and continuing on for a short distance, you arrive at the Second Hoppers. Here are seen the ruins of the old nitre works, leaching vats, pump frames and two lines of wooden pipes; one to lead fresh water from the dripping spring to the vats filled with the nitrous earth, and the other to convey the lye drawn from the large reservoir, back to the furnace at the mouth of the Cave.