or less charged with mineral matter.  Evaporation goes on slowly, leaving the mineral behind.  This in time makes the immense columns, many of them thousands of tons in weight, which serve to support the roofs over the vast chambers.  I recollect that at one point in the cave one of these columns is of such huge proportions that there is only a narrow passage left on either side of it.  Some of our party became satisfied with their explorations before we had reached the point to which the guides were accustomed to take explorers, and started back without guides.  Coming to the large column spoken of, they followed it entirely around, and commenced retracing their steps into the bowels of the mountain, without being aware of the fact.  When the rest of us had completed our explorations, we started out with our guides, but had not gone far before we saw the torches of an approaching party.  We could not conceive who these could be, for all of us had come in together, and there were none but ourselves at the entrance when we started in.  Very soon we found it was our friends.  It took them some time to conceive how they had got where they were.  They were sure they had kept straight on for the mouth of the cave, and had gone about far enough to have reached it.

CHAPTER XIV.

Return of the army—­marriage—­ordered to the pacific coast—­crossing the isthmus—­arrival at San Francisco.

My experience in the Mexican war was of great advantage to me afterwards.  Besides the many practical lessons it taught, the war brought nearly all the officers of the regular army together so as to make them personally acquainted.  It also brought them in contact with volunteers, many of whom served in the war of the rebellion afterwards.  Then, in my particular case, I had been at West Point at about the right time to meet most of the graduates who were of a suitable age at the breaking out of the rebellion to be trusted with large commands.  Graduating in 1843, I was at the military academy from one to four years with all cadets who graduated between 1840 and 1846—­seven classes.  These classes embraced more than fifty officers who afterwards became generals on one side or the other in the rebellion, many of them holding high commands.  All the older officers, who became conspicuous in the rebellion, I had also served with and known in Mexico:  Lee, J. E. Johnston, A. S. Johnston, Holmes, Hebert and a number of others on the Confederate side; McCall, Mansfield, Phil.  Kearney and others on the National side.  The acquaintance thus formed was of immense service to me in the war of the rebellion—­I mean what I learned of the characters of those to whom I was afterwards opposed.  I do not pretend to say that all movements, or even many of them, were made with special reference to the characteristics