1891.] ; Mineralogy and Petrography. 573 
types are chlorite and hornblende-schists, granulites, gneisses and por- 
phyroids, sericite-schists, and other foliated rocks, An important part 
of the study is that embracing the discussion of the effects of pressure 
upon the mineral constituents of the original rocks, and of the new 
structures produced in the secondary rocks. The new minerals formed 
during the production of the schists are albite, microcline, zoisite, 
garnet, quartz, hornblende, epidote, biotite, muscovite, sericite, rutile, 
anatase, and sphene. Each of these is carefully described, and the 
conditions under which it was formed are carefully examined. The 
genesis of the schistose structure is finely worked out, both macro- 
scopically and microscopically, and the mineral change that accom- 
panies the development of the foliation is well shown. A large body 
of green schists is thus proven to have been developed by pressure 
from massive rocks, just as the gabbro-diorites were formed from gab- 
bros in the Baltimore region. There are many interesting features of 
the Michigan schists that might be dwelt upon at some length did 
space permit, and many important mineralogical metamorphoses 
might be referred to. But no review, however full, can do more than 
Suggest the outline of the bulletin. It must be read to be understood. 
The many. good maps and illustrations and the nine lithographic 
plates of rock structures render great aid to the reader. It is evident 
that the schists of Michigan cannot grade into the overlying fragmen- 
tals, and since they are much more squeezed than these, that they can- 
not be of the same age.——An important communication, bearing 
upon the relation existing between dyke rocks and their corresponding 
Plutonic facies, has lately appeared under the names of Hunter and 
Rosenbusch,* who have discovered that one of the rocks occurring in 
dyke form in the elzolite-syenite region of the Serra de Tingua, 
Brazil, is a new type, which may be regarded as the equivalent of the 
plutonic elzolite-syenite. The rock has been called trachyte, phono- 
lite, and basalt by various writers, but the present authors have decided 
to give it a distinctive name, ‘‘ monchiquite,’’ from the locality in Por- 
tugal from whence the type was first described. The rock belongs 
among the camptonites. It is of a dark color, and is composed of a 
dense ground-mass holding small phenocrysts of amphibole, pyroxene, 
examined, the ground-mass is found to 
. 
mica, and olivine. Carefully 
* Miner. u. Petrog. Mitth., XI., 1890, p. 445: 
