PETROLOGICAL ABSTRACTS AND REVIEWS 275 
when consolidated produces breccias, the lighter ashes and dust, tuff. 
The term volcanic conglomerate should be restricted to water-laid con- 
glomerates consisting of volcanic material; volcanic agglomerate to 
the coarse material filling the upper portions of old volcanic conduits. 
Volcanic tuffs may consist of glass (vitric tuffs), crystals (crystal tuffs), 
or fragments of rocks which may be holocrystalline or partly glassy 
(lithic tufts). 
Under the head ‘“‘Vitric Tuffs’’ the formation of tuffs, the forms 
of the particles, the appearance of a thin section of consolidated tuff, 
the shapes of the individual dust particles, the texture of the rock and 
the magmatic relations of the material are considered, while under 
“Crystal Tuffs”’ the origin of the crystals, their form, and the inter- 
stitial fillings, and under ““‘Lithic Tuffs” the origin, appearance, and 
character are described. Although these type tuffs may occur, it is 
more common to find transition rocks. The author concludes his 
paper with a discussion of the alteration of tuffs, including their weather- 
ing and consolidation, devitrification, and metamorphism. 
Prirsson, L. V. ‘‘Geology of the Bermuda Island,” Amer. Jour. 
Sct., XX XVIII (1914), 189-206, 331-44, figs. 2, analysis r. 
This is a geologic and petrographic study of material obtained from 
a bore hole, 1,413 feet deep, in Bermuda. Roughly, the section, begin- 
ning at the top, shows chalky Bermuda limestone to 380 feet, sea-level 
being 135 feet below the surface. Between 380 and 500 feet the hole 
passed through fragmental volcanic material, greatly altered, soft and 
claylike with harder inclusions. From 590 to 695 feet the material 
is sand and gravel composed of water-worn volcanic débris. Beginning 
at 695 feet there is a series of lava flows, basaltic in character, dense 
and black to gray, and amygdaloidal at the tops. The separating lines 
between the flows are at 695, 850, 1,002, 1,080, 1,200, 1,385, and 1,413 
feet, the latter the bottom of the well. 
‘From the character of the material overlying the solid lava, the 
~ conclusion is drawn that Bermuda was once a volcanic island which was 
entirely cut away to the level of the sea by wave-action, and subse- 
quently formed the platform for the growth of a coral island. 
A petrographic study of the material collected from the well was 
made difficult by the fact that a churn-drill was used, consequently 
the material was in a finely divided state. The lava consists of two kinds, 
both belonging to the alkali series: (a) feldspar-free basalts, including 
