17 Class 4: Bonded yards or sheds for the storage of heavy and bulky imported merchandise. Warehouses of this class are used exclusively for the storage of heavy and bulky articles. The yards must be inclosed by substantial fences, not less than 12 feet in height, with entrance gates capable of being secured by customs locks. The collectors may send to such yards unclaimed or seized goods of the character above described. Stables or parts thereof may be bonded upon approval of the department for the storage of animals. Class 5: Bonded bins or parts of buildings or of elevators to be used for the storage of grain. The bonded portions must be separate from the rest of the building. Warehouses of class 4 or 5 may be bonded exclusively for the storage of goods imported by the proprietor thereof, in which case they are designated as ‘importers’ private warehouses.” Class 6: Warehouses for the manufacture in bond, solely for exportation, of articles made in whole or in part of imported materials or of materials subject to internal-revenue tax; and for the manu- facture for home consumption of exportation of cigars in whole of tobacco imported from one country. Class 7: Warehouses bonded for smelting and refining imported ores and crude metals for exportation or domestic consumption. Class 8: Bonded warehouses established for the purpose of cleaning, sorting, repacking, or otherwise changing in condition, but not manufacturing, imported merchandise, under customs supervision and at the expense of the proprietor. Such merchandise may be withdrawn for exportation, without payment of duties, or for con- sumption upon the payment of duties accruing thereon in its condition at time of withdrawal. The scouring or carbonizing of wool in such bonded warehouse is not considered a process of manufacture. Cartage and lighterage.—Cartage of merchandise in customs custody is of two kinds—(a) Government cartage, which must be done by a licensed customhouse cartman under contract for that purpose, and (b) importers’ cartage, which may be done by any licensed custom- house cartman. The cartage of package designated for examination at the appraisers’ stores or taken possession of for other reasons is done at the expense of the importer by a cartman licensed by the collector. Importers must designate on the entry of bonded mer- chandise the bonded warehouse in which they desire their merchandise deposited and the bonded cartman by whom they wish it to be con- veyed. An adequate system of receipts covering the transfer of merchandise between docks and bonded warehouses is provided for by the customs regulations. Cartmen give receipts to the importing vessel for all packages or merchandise in bulk delivered to them, and are held liable under their bonds for its prompt delivery and sound condition unless specially relieved of responsibility. FOREIGN TRADE ZONES