Geology of America. 75 
ber of the States, the Government has ordered geological sur- 
veys to be made at the public expense. This is a good ar- 
rangement, and peculiarly necessary in a country like the United 
States, where the field is immense, and the men of science 
few. Besides, a man clothed with public authority gets easier 
access to useful documents than an amateur ; his object is less 
likely to be misunderstood ; and being paid for his work, he 
does it systematically, instead of selecting special subjects of 
inquiry suited to his private convenience or his individuai 
taste. 
Valley of the Mississippi.—Nearly the whole of the vast basin 
of the Mississippi, from the Alleghanies to the Rocky Moun- 
tains, a space equal to two-thirds of Europe, is covered by a 
series of deposits, which has been divided into thirteen forma- 
tions,—the upper corresponding to the coal measures of Eng- 
land, the lower to the Devonians or Old Red Sandstone, the 
Silurians, and the Cambrians. The thickness of the whole is 
estimated at 40,000 feet, or. nearly eight miles ; and this is ex- 
clusive of the primary stratified rocks. The coal exists only 
in certain portions of the great basin. The Silurians have 
been identified by their fossils ; an interesting fact, when we 
consider that a space of 5000 miles intervenes between the Bri- 
tish and American Strata. Mr Murchison was highly grati- 
fied to find the British fossils in northern and central Russia, 
at the distance of 1200 or 1400 miles from the Silurian dis- 
trict of Wales; but their appearance on the west side of the 
Alleghanies, is still more important. It enables us to state 
that the same species of sauroid and shell-fish, and corals, had 
existed at the Silurian period from the latitude of 40, to that 
of 60, and from the Volga to the Mississippi. At the present 
day the range of species is much more limited. The testacea, 
zoophytes, and fish for instance, of the Red Sea, are as a group 
extremely distinct from those of the Mediterranean (Lyell’s Ele- 
ments, ii. p. 204.) 
The cretaceous formation has been found in the basin of 
the Mississippi, and identified by the fossils, but the rock does 
not assume the form of chalk—a case not uncommon. Patches 
of the oolite have been found in the same region ; and a stripe 
of tertiary deposits has been traced along the eastern coast 
