FV. Hayden on ihe Cretaceous rocks of the West. 171 
serves to augment the volume, so that a constant pressure ma 
in potash, and used double, the inner one coated with tallow, 
and when the apparatus was left to itself the pressure only va- 
ried a few millimeters in twenty-four hours, and could easily be 
kept perfectly constant by a few strokes of the air pump during 
a distillation. We will give the results of several series of dis- 
tillations made with the same material under different pressures. 
[To be concluded.] 
Art. XVIII.—Remarks on the Cretaceous rocks of the West known 
as No. 1, or the Dakota Group; by F. V. HAYDEN. 
THE Cretaceous rocks of the Upper Missouri have been sep- 
arated into five divisions, which have been a for the 
* Memoirs Am. Acad. Arts and Sci., vol. y, new series, also numerous papers by 
F, B. Meek and F. V. Hayden. 
t+ Proceedings Acad. Nat. Sci. Dec. 1861. 
