part of the
figure shows a similarly marked flag from the same formation at a point
about five miles north of the old Boquillas postoffice near Tornillo
Creek, east of the Chisos Mountains, in Texas. Here are seen the
original grooves made by the ice on a layer of muddy material later
buried. Slightly reduced.

[Illustration: PLATE II]

PLATE III

Plate III. Photograph of fossil casts of a close tangle of ice crystals
seen in a stony calcareous layer in the Eagle Ford shale in Walnut
Creek, about eight miles north of Austin, Texas. This tangle is closer
than any of the recent ice crystal marks figured here, but equally
closely grown crystals have been seen by the writer on frozen mud in
Illinois. Natural size. Compare with Plate VIII.

[Illustration: PLATE III]

PLATE IV

Plate IV. Photograph of fossil casts of ice crystals seen on some stony
flags in the upper part of the Eagle Ford at Fossil Knobs, about two
miles northwest of the Chisos Mine in Brewster County, Texas. These may
be characterized as relatively short and scattered. This shows ridges
projecting into the grooves formed by ice crystals on the surface of a
muddy layer originally underlying the layer photographed. Slightly
reduced.

[Illustration: PLATE IV]

PLATE V

Plate V. Photograph of fossil casts of ice crystals seen on the under
side of flaggy layer of calcareous sandy rock in the upper part of the
Eagle Ford at Fossil Knobs, about two miles northwest from the Chisos
Mining Company's property, Brewster County, Texas. It will be seen that
some of the crystals are gently curved. Similar curving crystals are
also seen in the figures showing recent growths at Rock Island,
Illinois. Compare with Plate IX. Slightly reduced.

[Illustration: PLATE V]

PLATE VI

Plate VI. Photograph of a thin flag of sandy limestone from the Eagle
Ford at Fossil Knobs in Brewster County, showing molds left by ice
crystals.

[Illustration: PLATE VI]

PLATE VII

Plate VII. Photographs of three fragments of flags showing casts of ice
crystals on the under side. All observations made on crystals of this
kind indicate local differences in the forms of ice crystals presumably
due to differences in the rate of freezing, in the texture of the mud
and probably in variations in water content of the mud. Some crystals in
the locality from which these specimens came, show pinnate secondary
growths. Specimens shown here are fr