EXPLANATION OF PLATE XXI.

A (one nicol) and B (x-nicols). Colloform gel banding; microcrystalline quartz and chalcedony; zonal growth lines in comb quartz; parallelism of comb quartz individuals. Gold Road, Ariz. (X 35.)

C (one nicol) and D (x-nicols). Fibrous chalcedony; crustification banding flamboyant quartz (at left of upper band, -marked 'r'). White Rock, Australia. (X 35.)

E (one nicol) and F (x-nicols). Micro-botryoildal gel structure, its preservation by inclusions in flamboyant quartz crystals; these crystals are unrelated to the structure of the original gel. Talisman Mine, New Zealand. (X 35.)

EXPLANATION OF PLATE XXII.

A (x-nicols). Feathered quartz with perfect core. Kingman, Ariz. (X 35.) B (x-nicols). Feathered cross effect when anomaly has not a perfect core. (X 108.)

C (x-nicols). Ideal view of cross effect (upper crystals); typical appearance of anomaly (lower crystal). Rawhide, Nev. (X 108.)

D (x-nicols). Typical feathered quartz prisms. Caledonian Mine, Thames, New Zealand. (X 36.)

E (x-nicols). Flamboyant quartz encrusting vein wall. Talisman Mine, Karangahake, New Zealand.

(X 37.)

F (x-nicols). Typical flamboyant quartz showing radial relief lines. Talisman Mine, Karangahake, New Zealand. (X 60.)

EXPLANATION OF PLATE XXIII.

A (x-nicols). Zonal markings by inclusions. Union Mine, Austin, Nev. (X 36.)

B (one nicol). Zonal markings by lines of relief, probably microscopic bands of chalcedony in this figure. Salisbury Gold Mining Co., W. Australia (X 106.)

C (one nicol) and D (x-nicols).

Phantom veinlets. Notice offset of

crystal at r. Union Hill Mine, Grass Valley, Calif. (X 37.)

E (x-nicols). Secondary enlargement of fragment in tuff. Jarbidge, Nev.

(X 77.)

F (x-nicols). Anhedral interlocking quartz. Alaska. (X 33.)

Alaska Treadwell Mine,