SHIP ROCK

volcanic neck with radiating dikes located in the northwest corner of New Mexico, U.S. The landmark stands 1,400 feet (420 m) above the surrounding area and was the basis for local Navajo legends. Solidified in the vent of an ancient volcano, the more resistant rock of the neck is all that remains after erosion. Types of ships The great majority of ships that are neither military vessels nor yachts can be divided into several broad categories: cargo carriers, passenger carriers, industrial ships, service vessels, and noncommercial miscellaneous. Each category can be subdivided, with the first category containing by far the greatest number of subdivisions. Service vessels The service ships are mostly tugs or towing vessels whose principal function is to provide propulsive power to other vessels. Most of them serve in harbours and inland waters, and, because the only significant weight they need carry is a propulsion plant and a limited amount of fuel, they are small in size. The towing of massive drilling rigs for the petroleum industry and an occasional ocean salvage operation (e.g., towing a disabled ship) demand craft larger and more seaworthy than the more common inshore service vessels, but oceangoing tugs and towboats are small in number and in size compared to the overwhelmingly more numerous cargo ships.