Ileview of liecent Geological Liferutnre. 123 
Museum d'Histoire Naturelle, Paris. 3me Serie, vi, pp. 209-308, avec 6 
planches des caracteres microscopiques, quarto, 1894.) This publication 
results from Prof. La Croix' connection .with the Geological Survey 
of France, in the prosecution of which he was intrusted with an 
examination of the eruptive and metamorphic rocks of the Pyrenees. 
While this embraces all that is known concerning the mineralogy of 
Iherzolyte, another contribution devoted to its geological relations wiU 
appear at a later date in the bulletins of the geological survey. This 
work is divided into three parts, viz.: 
1. Historical sketch and rapid review of the geographic distribution 
and the age of Iherzolite and of the rocks which accompany it. 
2. The mineralogical study of all these rocks. 
.3. Description of the metamorphic phenomena produced by its con- 
tact with the secondary rocks. 
Lherzolyte is a yellowish green, rather coarse-grained hard rock, eas- 
ily disintegrated by atmospheric agents, consisting of olivine, enstatite 
(bronzite), chromiferous diopside and a chromiferous spinel, picotite — 
an eruptive, basic rock which, in the Pyrenees, has always heretofore 
been considered of a later date than a certain white crystalline lime- 
stone, and thus later than the Lias, or even of the Neocomien. Obser- 
vations, however, made l)y the author, prove it is older than this lime- 
stone, which contains fragments of it in a rounded form. It is later, 
however, than another limestone which it cuts which contains fos- 
sils of the middle Lias. The ease with which the rock separates 
into its separate constituent elements has contributed to the exact- 
ness and the completeness of the study of the crystalline and optic 
characters. The rock is sometimes porphyritic with large crystals of 
bronzite and of diopside, and it sometimes contains hornblende. It 
has been affected by mechanical action, resulting in a "mortar struc- 
ture," and in a secondary pseudo-porphyritic appearance. 
Among the secondary mineralogical changes the author mentions 
rubifaction, serpentinization and amphibolization. These are very char- 
acteristic at the outcrops, which take a dark, rusty color greatly in con- 
trast with the surrounding white limestone. In this change olivine 
plays a leading part. It turns red, by absorbing an ochreous-yellow 
substance which finally rejjlaces it entirely. This is then easily removed 
by rains and forms a yellowish mud. The cavities left by the removal 
of the olivine bring the other minerals into relief, and they vmdergo a 
slow loosening disintegration which serves to allow the extraction of 
each separately. In the interior of the rock, however, these minerals, 
on fresh fracture, can with difficulty be distinguished from each other 
without microscopic examination. 
Serpentinization has in some places gone on on a large scale, but 
frequently is confined to fissures. 
Amphibolization, in its simplest form, is uralitization, or a change 
from pyroxene. It also takes place in the bronzite. Hornblende in 
certain places is so common that the author describes and names the 
rock containing it, as a special variety of Iherzolyte. It is interesting 
