National Geographic : 1925 Aug
Photograph by Ebro Observatory ALTO-STRATUS (LOWER PART OF ILLUSTRATION) This form consists of "a thick sheet of gray or bluish color, sometimes forming a compact mass of dark-gray color and fibrous structure. At other times the sheet is thin, resembling thick cirro-stratus (see page 182), and through it the sun or the moon may be seen dimly gleaming, as through ground glass." Photograph by A. J. Weed ALTO-CUMULUS : SOMEWHAT RAGGED Alto-cumulus clouds are "largish globular masses, white or grayish, partly shaded, arranged in groups or lines, and often so closely packed that their edges appear confused. The detached masses are generally larger and more compact at the center of the group, but the thickness of the layer varies."