1880.] A485 [Crosby. 
tained in a large measure their original structural simplicity and un- 
altered condition, making it impossible to question the Eozoic age of 
the most at least of the crystalline rocks. 
CRYSTALLINE FORMATIONS OF BRAZIL. 
For the little that is definitely known concerning the crystallines 
of Brazil we are indebted mainly to the labors of the lamented Prof. 
Hartt and his co-workers of the Brazilian Geological Commission. 
These results, as recently summed up by Mr. O. A. Derby,! show that 
the older rocks of the empire may be “ naturally divided into two 
very distinct series, of which one, the most ancient, consists of crys- 
talline rocks, including gneiss, gneiss-granite, and syenite, and the 
other, more modern, of altered, but in general non-crystalline rocks, 
consisting of quartzites, metamorphic schists, and crystalline lime- 
stones.”’ 
So far as studied, these great divisions of the Brazilian Eozoic 
show widely dissimilar characteristics in all parts of the Empire. The 
gneisses in the older series are described as containing much red or 
flesh-colored feldspar, and as being often granitoid, or obscurely 
stratified, porphyritic and schistose. ‘The syenites consist typically 
of flesh-colored feldspar and hornblende, with little or no quartz ; 
and are probably both exotic and indigenous. Epidotie rocks are 
abundant in some parts. ‘The crystalline series is also said to be ac- 
companied by an abundance of exotic rocks, including porphyry (fel- 
site), diorite, and basaltic varieties. Liais? is very confident that 
these various eruptive rocks, especially the granite and syenite, are, 
frequently at least, of metamorphic origin, arising among the stratified 
terranes as the result of excessive alteration of the latter; the gneiss 
and granite, for instance, being identical in age and origin as well as 
in composition, and differing only in the degrees of metamorphism 
which they have experienced. ‘This series was referred to the Lau- 
rentian by Prof. Hartt; and this correlation was confirmed by Dr. 
Hunt, after an examination of the specimens collected by Prof. Hartt. 
Limestones are sparingly associated with the gneisses.? These are 
1Proc. Am. Phil. Soc. 1879, pp. 155-178 and 251-258. 
2Climats, Géologie, Faune et Géographie Botanique du Brésil par Emmanue 
Liais. Publié par ordre du Gouvernement Impérial du Brésil. Paris, 1872. 
3 American Journal of Science, X1x, 1880, pp. 324-327. 
