1. Lamellar. 2. A lamellar or spherical nucleus, with spinous ramifications in different places. 3. Fine spiculx or six-sided prisms. 4. Hexagonal pyramids. 5. Spiculx, having one or both extremities affixed to the centre of a lamellar crystal.
1. Lamellar crystals. 1\lr. Scoresby assures us that the varieties or this modification are very numerous, occurring abundantly at all temperatures, and being very thin and transparent, and of a highly delicate structure. These, he says, may be divided into several distinct species.
a. Stellilorm; having six points radiating from a centre, with parallel collateral ramifications in the sante plane. This species, represented in Plate CCCCLXXXVIII. Fig. 1. is the most general form met with. It varies in size from the smallest speck, to about. one-third or an inch diameter. It occurs in greatest profusion when the temperature approaches the freezing point.
b. Regular hexagon. This occurs in moderate as well as in the lowest temperatures; but it becomes more delicate and thin, and diminishes in size as the cold increases. Some specimens consist or simple transparent plates, (Fig, 23.) others are beautifully variegated, within the perimeter, by white lines, form ing smaller hexagons or other regular figures, in im mense variety; Fig. 25, 27, 28, 30; Fig. 49, Re. The size of this species is from the smallest visible speck to about one-tenth of an inch diameter.
c. Aggregations of hexagons. This beautiful spe cies admits of immense variety. It occurs chiefly at low temperatures, and presents great limits of dimen sions; Figs. 2, 9, 10, 14, 17; and Figs. 29, 34, 37, 39. &c. afford examples or this species.
(I. Combinations of hexagons, with radii or spines, and projecting angles. This constitutes the most ex tensive species in the arrangement; and affords some of the most beautiful specimens. Fig. 7, is an elegant combination of spines and hexagons; and Figures 50, 55, 58, 59, 60, &c. together with all the others distin guished by the letter s after the numbers, constitute a novel and beautiful varitty, which I have only once observed. The parallel lines that appeal' in these figures, are not intended as shadings, but actually oc curred in the crystals, though with this difference, that the lines which appear black in the plate, were all white in the originals. Figures 56, 63, 64, and
93, were opaque crystals, and were not so thin'as the others.
The latter of these, as well as Fig. 94, each having twelve spine, appear to be accidental varieties, and are produced probably by the correct application or two similar crystals upon one another.
2. ./ lamellar or spherical nucleus with spinous rami fications lit different planes.—This genus not being easily represented, is not illustrated by any•figure. It•consists of two or three species.
a. The fundamental figure, consisting of a lamellar crystal or any of the species above described, from the lateral and terminal planes of which arise small spines, similar to the collateral ramifications of Fig. 1. These spines arise either from one or both of the lateral planes or principal surfaces, or from both lateral and terminal planes; and always maintain the usual angle of ith the plane from which they take their rise.
The diameter of this figure sometimes exceeds the fourth of au inch. This species falls most frequently at a temperature of 20° or 25°.
b. Having a spherular nucleus, giving rise to radii in all directions. In the former species, the central figure is a transparent crystal; in this it consists of a small rough white concretion. The spines or radii are similar in both figures. The diameter of this seldom reaches a quarter of an inch. The form is echinose. This species falls when the degree of cold is near the freezing, and sometimes in rather low temperatures.
3. Fine spicuke or are sometimes very delicate and crystalline; at others NS bite and rough. The finest specimens, which re semble white hair cut into lengths not exceeding a quarter or an inch, are so small and clear, that the exact figure is not easily determined; and the larger exhibit a fibrous or prismatic structure. Some of' these are occasionally the third of an inch in length. This genus is only seen when the temperature is near the freezing point. When the thermometer is about 28 degrees, the finer specimens occur; when about the freezing, the coarser appear. The latter arc very common (luring fog showers, and appear to be com posed of aggregations of the frozen particles of the fog, and to have their origin in the lower parts of the atmosphere.