Limits of the Chalk- Formation. 141 
chalk still appears at 54° north latitude, it descends, as may 
be seen by M. Murchison’s beautiful geographical map, by 
Mohilew and Orel, half a degree to the south of Moscow, then 
to Simbirsk and the Volga, as far as the Caucasus. It was al- 
together an unexpected event that Messrs Murchison, Ver- 
neuil, and Keyserling again discovered this chalk on the 
banks of the River Ural, 20 German miles below Oren- 
bourg, at 513° north latitude. The Muchodjar mountain ap- 
pears to be the limit of these formations towards theeast. The 
prodigious extent of Siberia, from the Ural as far as Ochotzk, 
and from the Altai to the Icy Sea, has been so well and 
carefully examined by mining engineers, naturalists, and 
searchers for gold, that we have reason to doubt the exist- 
ence of chalk strata over this vast extent of country. 
Everywhere within these limits, the upper chalk appears 
to be the bed distinguished principally by Gryphwa vesicu- 
laris, Belemnites mucronatus and mamillaris, Inoceramus Cu- 
viert and Cripsii, Ostrea diluvii, Terebratula carnea and 
semiglobosa, Ananchytes ovata, Galerites vulgaris and albo- 
galera, and their analogues. The old chalk strata appear as 
we descend to the south ; and in the Caucasus and Daghes- 
tan, these ancient (neocomian) beds seem to reach, according 
to the excellent researches of M. Abich, a thickness of nearly 
5000 feet. It is as if avast wave had descended from the 
summit of the Caucasus, extended itself forwards, and ex- 
pired by degrees on the plain, at the limits of the ancient 
rock formations. 
On the other side of the ocean, the chalk-formations ter- 
minate in the Atlantic portion of the United States, before 
reaching the city of New York, so that their limit scarcely 
rises to 40° of north latitude, 16° less than in Europe. In 
Kentucky and Tenessee, this limit is below 37° north latitude. 
But it is otherwise in the Missouri, where the great river of 
that name flows without interruption from the foot of the 
Rocky Mountains, over an extent of 1400 miles, through for- 
mations of chalk, at least as far as the mouth of the River 
Sioux. This, at all events, is what we learn from the 
Memoirs and Collections of Prince Neuwied, and the Report 
of Nicollet, the astronomer. It appears, then, that, in the 
