1877. ] Geology and Paleontology. 47 
two articles in the Geographical Magazine for October, by Mr. Raven- 
stein, accompanied by four maps exhibiting the spread of Mohamme- 
danism, the political divisions, the comparative density of population, 
and the nationalities ; and the History of the Mongols from the Ninth to 
the Nineteenth Century, by Henry H. Howorth. — O. T. Mason. 
GEOLOGY AND PALZHONTOLOGY. 
THE GEOLOGICAL SURVEY IN CHARGE oF Pror. F. V. HAYDEN. — 
The productiveness of the work pursued in America by Professor 
den, the greatness of the results obtained by this savant and the 
collaborators whom he has associated with him, the hope and expecta- 
tion of having science enriched by new discoveries of which those of 
these last times seem but a prelude, — all these considerations have 
deeply impressed the French savants, who attentively watch the re- 
searches of every kind in geography, physics, botany, zoölogy, and 
especially geology and palæontology, pursued through the unexplored 
Territories of the United States west of the Mississippi, and towards the 
Rocky Mountains. It would be impossible to trace out, even in a sum- 
mary, what is the most striking and interesting part in the undertaking 
of Professor Hayden, and I must merely mention some essential points 
which from the speciality of my studies I am prepared to appreciate to 
their full value. It is certain, first, that the Yellowstone or Geyser 
region, recently surveyed and preserved by the wisdom of the Federal 
government against the danger of devastation, put to the disposition of 
science the exposition of an assemblage of phenomena of the highest 
interest. Their examination will serve to explain the mode of forma- 
tion of the lacustrine deposits of Europe, where the geyserian action is 
so remarkably visible. Henceforth it will be easy to follow the proceed- 
ings formerly employed by nature on the European Continent, and 
which now are in full action in the central part of the American Union. 
It is also evident to the geologist who considers the general classifica- 
tion of the formations, as it is fixed from the order of the materials as 
they exist in Europe, that a great revolution is preparing in geology 
from the discoveries in regard to the stratigraphy of the Territories re- 
cently explored under the direction of Dr. Hayden. The Dakota group 
and the lignitic formation constitute, in fact, two systems of an enormous 
power, wherein the fresh-water formations of an uncommon thickness 
are directly superposed on the marine beds, or in alternation with them. 
hese two systems the one is incontestably cretaceous, the other as — 
incontestably tertiary, and both, equally rich in fossils, animal and vege- 
table, are so intimately bound together that the passage from the one to 
the other is by a series of degrees without interruption or gap. 
Now this is indeed a fact of immense importance in this, that it dis- 
= Proves all that was supposed to have been observed positively in 
~ “arope in generalizing local and partial phenomena. In the minds of 
