Height of base: 17,000 to 35,000 ft Colour: Composed of ice crystals, therefore white. Shape: Patches or sheet of very small elements in the form of grains or ripples or a honeycomb. When viewed from the ground, the size of individual elements will have an apparent width of no greater than the width of a little finger at arm's length. Other features: Sometimes its appearance in a regular pattern of 'waves' and small gaps may resemble the scales of a fish, thus giving rise to the popular name 'mackerel sky'. (this name may also be given to high altocumulus clouds).