1880.) 487 [Crosby. 
formably upon, the first or highly crystalline series. The principal 
rocks of the second series are the quartzites; these frequently pass 
into ordinary sandstone and include many varieties; that best known, 
however, is the flexible sandstone or itacolumite, which is commonly 
and, as it seems, correctly regarded as the source — “die Mutter- 
gesteine’’ — of the diamond. Interstratified with the quartzites, and 
ranking next to them in importance, are the rocks classed as hydro- 
mica or talcoid schists. These likewise present many phases, and, 
although genuine hydromica schist is undoubtedly the prevailing 
type, argillaceous, chloritic, hornblendic and other rocks appear to be 
included, as well as much true argillite. The schists are often ferru- 
ginous, and associated with these and the quartzites are heavy beds 
of crystalline limestone and bedded iron ores, the itabirite being an 
interesting form of the latter. 
Stratified felsites are also said to form a part of the second series ; 
these are likewise often red and ferruginous; but they are, apparently, 
less widely distributed than the preceding, and are not intimately as- 
sociated with the schists and limestone. The stratification of the 
felsites is unquestionable since they are interstratified with quartz- 
ites, and sometimes, according to Mr. Derby, ‘‘ show lamination, 
wave and ripple marks as clearly as any modern sandstone.’’ 
In the Amazonian region, the rocks of the second series are most 
favorably exposed in the rapids of the Tocantins, Tapajos and Trom- 
betas Rivers. On the Tocantins the strata are compact and granu- 
lar quartzites, hydromica and other schists and crystalline limestones; 
while on the Tapajos and Trombetas the felsites predominate, the 
quartzite is compact (felsitic?) and the schists and limestones are en- 
tirely wanting. Prof. Hartt believed the beds on the Tocantins to 
be newer than those on the other streams named, and this opinion is 
shared by Mr. Derby. In other words, the upper member of the 
Eozoic is divided by these geologists into two parts, the first or oldest 
including the felsites and compact quartzites, and the second the ita- 
columites, schists and limestones. To my mind, however, one of two 
things seems probable; either the felsite group belongs to the older 
or crystalline series, in which case it may be correlated with the un- 
questionably ancient petrosilex (felsite) and associated rocks of south- 
ern Brazil, Uruguay and Chili, the true Huronian; or else the so- 
called felsites are merely re-composed rocks, owing their Huronian 
characteristics to derivation alone. ‘The relations of this group to 
the Tocantins series favor the former view, and the distinctness of the 
stratification in the felsites the latter. 
