5^"- The American Geologist. January, i903.. 
"j>acytcs. The medium type of these rocks presents the greatest 
analogy, in outer aspect, with the csterellyte of San Raphael. With the 
naked eye can be distinguished large crystals of quartz with double 
terminations, hornblende biotite, hypersthene and plagioclase scattered 
in a microcrystalline paste of a bluish gray color. The rocks of Grand 
Piton, of the rocky Piton of Morne near Macouba, afford good ex- 
amples. 
"With the microscope it can be seen that the hornblende and the 
biotite are in course of resorption, the feldspars are much zoned, gen- 
erally with the central part most basic, but often also with a succession 
of zones alternating of two different feldspars. These feldspars are 
nearly always flattened parallel to g'\ with a combination of Carlsbad, 
albite and pericline twinning. Their determination is therefore quite 
easy. The most common types are labradorite with 60 per cent of an- 
orthite, and andesine. Vitreous inclusions with bubbles are abundant, 
ns in all the other volcanic rocks of Martinique. All these phenocrysts 
have a great tendency to unite together and form small segregations. 
The hornblende crystals are frequently ophitic with the feldspars. 
"The paste of the rock is constituted essentially of very small feld- 
pathic microlites, often themselves zoned, andesine and oligoclase. They 
are accompanied by quartz, sometimes granular, sometimes poecilitic : 
frequently there exists numerous microlites and crystallites of hypers- 
thene. A considerable amount of titanic magnetite is seen sometimes in 
the microlites and sometimes in the phenocrysts. 
"Andesytes with hypersthene. The petrographic type which appears 
to be the most widely extended consists of acid andesytes of a light 
color, often having a porous or scoriaceous paste, rough to the touch, 
Intt which, in certain cases, is more compact and acquires a dark color 
in consequence of the abundance of vitreous matter. These rocks are 
andesytes with hypersthene in wdiich the rhombic pyroxene is some- 
times accompanied by a little augite. The phenocrysts are, besides, 
formed of plagioclase of the andesine group. They are much zoned, 
but much less than in the labradorites. All these crystals are dissemin- 
ated in a glassy material which is more or less abundant, the feldspar 
microlites of which give extinctions that are sometimes longitudinal 
and sometimes oblique, only rarely reaching twenty degrees. (Carbet 
Laillet river, west flank of Mont Pelee, environs of St. Pierre, of 
Precheur etc.). 
"In several localities the glassy matter is replaced in part by globu- 
lar quartz sponges, the secondary character of which does not appear 
doubtful. (Upper valley of Pirogues, summit of Morne Jacob, etc.) 
"Hypersthene lahradorytcs. These rocks are distinguished, generally 
by the naked eye, from the andesytes liy their doleritic aspect; they arc 
usually of a dark gray color and more or less compact. Under the mi- 
croscope it can be seen, further, that the hypersthene is often sur- 
rounded by the augite with their axes parallel. Finally, sometimes 
olivine is apparent. The plagioclases are more zoned than in the pre- 
