The internal formation and design of the snow crystal is of great importance and interest, and the delicately etched markings which occur upon their surfaces, and are so well brought out in the photo-micrographic illustrations, are due to certain minute air inclusions or small air tubes. When the light falls upon the crystal, these air tubes appear as dark tracings or lines and shadings and go to form and carry out the design of each individual crystal.
63. Solid, big storm type
64. A very symmetrical crystal
65. High altitude crystal
66. Freak crystal formed by broken sections uniting
During great snowstorms the winds within such storms blowing spirally inward toward the storm centre near the earth, and at the same time upward and outward, above, exert the vast powers of bringing together the material, the water vapours, which in conjunction with the icy breath of the raging blizzard, perfects the formation of the snow crystal.