Many astronomers, including a number who are not in sympathy with the above view, believe that snow and ice exist on the moon, even though water in the form of liquid and vapor is not observable. All the extremely brilliant portions of the surface, according to some astronomers, are covered with snow and ice. Certainly, some portions of the moon's surface reflect sunlight as brilliantly as if they were covered with freshly fallen snow, while other portions appear to be black by contrast. There also appears to be evidence that certain small markings, described as crater-cones and resembling our terrestrial volcanoes more than any other lunar feature, are at times temporarily obscured from view by a veil of vapors. Many observers believe that these crater-cones are active volcanic vents, and that there is considerable volcanic activity still taking place upon the moon.