Reviezv of Recent Geological Literature. 389 
It is useless to attempt to fully analyze this work. A simple men- 
tion of the secondary minerals discovered in these sedimentary strata 
will convey but an imperfect idea of the transformations that are de- 
scribed. Glauconite figures very largely, also quartz and the com- 
pounds of lime; among the species mentioned being orthoclase, gyp- 
sum, calcite, leverrierite, opal, pyrite, limonite, chalcedony, chert. 
Amongst the clastic minerals are mentioned zircon, tourmaline, 
(these two also sometimes apparently formed /;/ situ') rutile, mag- 
netite, orthoclase, plagioclase, anatase, brookite, chlorite, staurotide, 
garnet, apatite, corundum, ilmenite, disthene, and several others un- 
determined. A plate is devoted to the microscopic crystals. Their 
forms are so perfect that nearly all of them appear not to have sufifered 
any transportation, a fact which suggests that many if not all of them 
are indigenous. 
The author has given much time to the study of the various forms 
of glauconite and to the question of its origin. He brings to light 
some new facts and verifies others not well known. Amongst the 
characters of this mineral he emphasizes the following: With gen- 
erally rounded forms and olive green color, its grains are also some- 
times black; in thin section they vary from yellowish green to dark 
green with specific gravity from 2.2 to 2.83. Most glauconite is 
homogenous in structure, but it is sometimes granular, globular and 
concretionary. It also acts as a pigment in a manner similar to 
limonite, when it is impossible to separate it from the siliceous or 
argillaceous substratum which it colors. It is cleavable, as shown 
by the author in 1893, a fact which has since been recognized by La- 
croix who has determined the basal cleavage (001) similar to that of 
the micas and chlorites. This cleavage is difficult, fine or coarse, in- 
equally spaced, rare or frequent. The partings are rarely straight, 
being more often slightly sinuous or wavy. They are parallel or con- 
vergent; they even cut each other, when they are very irregular. 
These features are illustrated by figures. 
Glauconite sometimes includes mineral and organic substances, 
the former being usually quartz (which very rarelj' is traversed by 
rutile) feldspar and calcite, the latter microscopic forms and frag- 
ments of foraminifera and radiolarians. Sollas has also noted cocco- 
liths and coccospheres while Murray and Renard foimd in the glan- 
conite collected by the Challenger, particles of quartz, magnetite and 
other minerals. 
The cleavable grains of glauconite are sensibly polychroic. This 
was announced by Cayeux in 1892, and, as with black mica, the great- 
est absorption takes place when the cleavage is parallel to the 
principal section of the analyser. The mineral is then dark green, 
and when perpendicular to the cleavage its color changes to light 
yellow. 
By the aid of studies of Caldcron and Chaves, and especially of 
♦Mineralogie de la France et de ses colonies, I 407. 
