Marcw 1, 1901.] 
or even tertiary. To refer it to the latter age 
would not, however, help the hypothesis here 
discussed, since there is no evidence whatever 
of its being of marine origin, and its northward 
extension well into the heart of central Brazil 
makes it embrace a very considerable portion 
of the Archamazonia faunal region of Dr. von 
Ihering. 
The heavy trap dykes and sheets of this for- 
mation give very marked topographical fea- 
tures (lines of escarpments and obstructions in 
rivers) by which it can be traced even in re- 
gions that have not been geologically examined, 
and for some years I have occupied myself in 
tracing its distribution through such chance in- 
formation and specimens as were obtainable 
from regions not personally known to me. 
Particularly valuable for this purpose was the 
material which for years has been accumulating 
in the Museum National of Rio de Janeiro and 
which for the region under discussion is especi- 
ally important and authentic, since it contains 
a complete duplication of the material collected 
by Sellow on which Weiss’ paper, the most im- 
portant that has yet appeared on the geology 
of Rio Grande do Sul and Uruguay, was based. 
Without going into detail, suffice it to say that 
there is evidence that I consider sufficient to 
establish the general fact that this formation 
extends without a break and in the form of a 
great tableland, from 600 to 1,000 meters high, 
from near the headwaters of the Paran4 in 
southern Goyaz and western Minas Geres to 
the line of escarped hills that cross oearly in 
the middle, the State of Rio Grande do Sul 
from east to west. ‘T'o the south of this line, 
which seems to be a giant fault, the formation 
lies lower and has been much denuded, so that 
it is frequently interrupted by areas of older 
rocks appearing from underneath, but thus far 
no evidence whatever has been presented of 
the occurrence of any overlying formation of 
marine origin. 
Of special significance for our present purpose 
is the fact that the falls and rapids of the river 
Uruguay, down to the Brazilian limit and be- 
yond, are composed of the hard traps of this for- 
mation which would thus present a barrier to 
the sea which in tertiary times undoubtedly oc- 
cupied a part of the Argentine province of 
SCLENCE. 
349 
Entre Rios. The only point where the deposits 
of this sea are known to extend to the eastern 
bank of the Uruguay is near the town of Col- 
onia, too far south to suit the hypothesis here 
discussed. Topographically considered, the 
only line in which there was a possibility of a 
break across this barrier is a depressed area in 
front of the above mentioned line of escarp- 
ments, occupied by parts of the valleys of 
the rivers Ybicuhy, flowing westward to the 
Uruguay, and Jacuhy, flowing eastward to the 
Atlantic. These two valleys are, however, 
separated by a considerable spur that unites 
like an isthmus the highlands of the upper 
Uruguay basin with those of southern Rio 
Grande do Sul and Uruguay. Thus far no 
evidence has been presented that this isthmus 
was ever submerged, or that the depressed 
portions of the Ybicuhy and Jacuhy valleys 
are occupied by other than fluvial deposits. It 
is quite possible that in secondary or tertiary 
times an arm of the sea may have extended 
into the region of the lower part of the present 
Jacuhy valley, but if so there is slight proba- 
bility that it extended westward into those of 
the Ybicuhy and Uruguay, and even if such 
a connection be admitted it could only have 
been a narrow strait quite incapable of produc- 
ing the ‘collosal’ faunal difference that it is 
attempted to explain. Speculation as to the 
probable existence of this strait is, moreover, 
quite gratuitous, since, if I rightly understand 
Dr. von Ihering, its position is entirely within 
his Archiplata sub-region. 
; ORVIILLE A. DERBY. 
SAo PAULO, BRAZIL, 
Jan. 8, 1901. 
GEOLOGICAL MAP OF EUROPE. 
WuHarT has become of it? Why does Dietrich 
Reimer not publish it? 
Wm. A. INGHAM, 
Ex-Secretary Penna. Geol. Survey. 
NOTES ON INORGANIC CHEMISTRY. 
ROCK FORMATION. 
AN important contribution to the study of 
solid solutions has been made by Professor W. 
Spring in the Revue Générale des Sciences, under 
the title of ‘The Plasticity of Solid Bodies and 
