190 REVIEWS 
as well as the unknown deposits represented by the great unconformities 
that lie between these. The use of Proterozoic for these four systems 
as a group implies that taken together they are regarded as similar in 
importance to the Paleozoic, Mesozoic, and Cenozoic groups. To 
include the still greater Archean series, with its unknown extension 
downward, under the term Proterozoic is to introduce a usage more 
unfortunate than that which preceded the adoption of the term Pro- 
terozoic. The authors of this monograph have always stood for a 
sharp line of demarkation between the Archean and other rocks of the 
pre-Cambrian. It would have been easy to have said Proterozoic and 
Archean and thus to have given to the group included under the name 
Algonkian the dignity to which it is thought to be entitled by those 
who use the term Proterozoic for it. 
In the account of the great unconformity between the Upper 
Huronian and underlying rocks, given on p. 619, those who have held 
that the term Animikie should be applied to this as a distinct system, 
separated from the Huronian, will find much to justify their views. 
In conclusion I would state that this monograph, aside from a few 
points, mentioned, is logically arranged and very clearly written and, 
considering the number, variety, and excellence of the illustrations and 
having regard for the amount of detailed work, the results of which are 
here given, it must be considered as one of the finest publications of the 
Geological Survey. 
E. S. Moore 
“Versuche itiber Umbkristallisation von Gesteinen im _festen 
Zustande.’? Von F. LEEWINSON LeEssinc. Centralblatt fiir 
Min., etc., No. 19, (October 1, 1911), pp. 607-14... Figs’7. 
The experiments were planned to test the validity of the assump- 
tion that certain schists and contact metamorphic rocks have developed 
through the recrystallization of solid phases of previously existing rocks. 
A hand specimen of dunite and another of pyroxenite were subjected to 
a temperature of from 1,200 to 1,300° for nine months without showing 
signs of melting. ‘The observed changes were textural, mineralogical, 
and chemical. The pyroxenite became a porous, coarse-grained aggre- 
gate of yellow, monoclinic pyroxenes spotted with ferric oxide grains. 
The olivine of the original rock had completely disappeared. The 
dunite was changed from an aggregate of angular and rounded colorless 
olivine grains interspersed with bunches of serpentine to a rock in which 
no serpentine was visible, but in its place were groupings of colorless 
