"'There are three kinds of salt,' said the guide. 'One that is called green salt contains five or six per cent. of clay, and has no transparency; it is cut into blocks and sent to Russia exactly as it comes from the mine. The second quality is called _spiza_, and is crystalline and mixed with sand; and the third is in large masses, perfectly transparent, having no earthy matter mingled with it. The salt is found in compact tertiary clays that contain a good many fossils; the finest salt is at the lowest levels, and the poorest at the higher ones.' "Well, here we are at the top of the shaft, tired and hungry, and excited with the wonderful things we have seen. The visit to the salt-mines of Wieliczka is something to be long remembered." * * * * * Since the visit herein described, the manner of working the salt-mines of Wieliczka has undergone a decided change. Owing to the influx of a stream the lower levels of the mines were flooded, and for some time remained full of water. In order to free them it was necessary to introduce powerful pumping machinery of the latest designs, and also to replace the old hoisting apparatus with new. Horse-power was abandoned in favor of steam, both for hoisting and pumping; new precautions were taken against fire; all improved systems of mine-working were tested, and those which proved useful were adopted; and to-day the mines of Wieliczka may be considered, in every respect, the foremost salt-mines in the world. CHAPTER II. LEAVING CRACOW.--THE RUSSIAN FRONTIER.--THE POLICE AND THE CUSTOM-HOUSE.--RUSSIAN CENSORSHIP OF BOOKS AND PAPERS.--CATCHING A SMUGGLER.--FROM THE FRONTIER TO WARSAW.--SIGHTS AND INCIDENTS IN THE CAPITAL OF POLAND.--FROM WARSAW TO ST. PETERSBURG. [Illustration: OUTER WALL OF CRACOW.] The sun was setting as our friends reached Cracow, on their return from Wieliczka. The walls of the city were gilded by the rays of light that streamed over the hills which formed the western horizon. In all its features the scene was well calculated to impress the youthful travellers. Frank wished to make a sketch of the gate-way through which they passed on their entrance within the walls, but the hour was late and delay inadvisable. The commissioner said he would bring them a photograph of the spot, and with this consolation the young man dismissed from his mind the idea of the sketch. All retired early, as they intended taking the morning train for the Russian frontier, and thence to Warsaw. They were up in good season, and at the appointed time the train carried them out of the ancient capital of Poland. [Illustration: CUSTOM HOUSE FORMALITIES.]